UNDERWRITING AGREEMENT

Exhibit 1.1

7,625,110 Shares

SAVVIS, INC.

Common Stock (Par Value $0.01 Per Share)

UNDERWRITING AGREEMENT

January 17, 2007

January 17, 2007

Morgan Stanley & Co. Incorporated

Goldman, Sachs & Co.

Lehman Brothers Inc.

Ladies and Gentlemen:

MLT, LLC, a Delaware limited liability company (the “ Selling Shareholder ”), a stockholder of SAVVIS Inc., a Delaware corporation (the “ Company ”), proposes to sell to the several Underwriters named in Schedule I hereto (the “ Underwriters ”), an aggregate of 7,625,110 shares (the “ Shares ”), of the common stock, par value $0.01 per share, of the Company, (the “ Common Stock ”).

The Company has filed with the Securities and Exchange Commission (the “ Commission ”) a registration statement on Form S-3 (File No. 333-136028), including a prospectus, relating to the Common Stock (the “ Shelf Securities ”), including the Shares, to be sold by certain stockholders of the Company. The registration statement as amended at the time it becomes effective, including the information (if any) deemed to be part of the registration statement at the time of effectiveness pursuant to Rule 430A or 430B under the Securities Act of 1933, as amended (the “ Securities Act ”), is hereinafter referred to as the “ Registration Statement ”, and the related prospectus covering the Shelf Securities dated January 4, 2007 is hereinafter referred to as the “ Base Prospectus .” The Base Prospectus, as supplemented by the prospectus supplement specifically relating to the Shares in the form first used to confirm sales of the Shares (or in the form first made available to the Underwriters by the Company to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “ Prospectus ,” and the term “ preliminary prospectus ” means the Base Prospectus as supplemented by the preliminary prospectus supplement dated January 8, 2007. If the Company has filed an abbreviated registration statement to register additional shares of Common Stock pursuant to Rule 462(b) under the Securities Act (the “ Rule 462(b) Registration Statement ”), then any reference herein to the term “ Registration Statement ” shall be deemed to include such Rule 462(b) Registration Statement.

For purposes of this Agreement, “ free writing prospectus ” has the meaning set forth in Rule 405 under the Securities Act, “ Time of Sale

Prospectus ” means the preliminary prospectus together with the free writing prospectuses, if any, each identified in Schedule III hereto and the information set forth on Schedule III-A hereto, and “ broadly available road show ” means a “bona fide electronic road show” as defined in Rule 433(h)(5) under the Securities Act that has been made available without restriction to any person. As used herein, the terms “Registration Statement,” “preliminary prospectus,” “Time of Sale Prospectus” and Prospectus shall include the documents, if any, incorporated by reference therein. The terms “ supplement, ” “ amendment ” and “ amend ” as used herein with respect to the Registration Statement, the Base Prospectus, the preliminary prospectus, the Time of Sale Prospectus, the Prospectus or any free writing prospectus shall include all documents subsequently filed by the Company with the Commission pursuant to the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), that are deemed to be incorporated by reference therein.

1.     Representations and Warranties of the Company . The Company represents and warrants to and agrees with each of the Underwriters that:

(a)    The Registration Statement has become effective; no stop order suspending the effectiveness of the Registration Statement is in effect, and no proceedings for such purpose are pending before or, to the knowledge of the Company, threatened by the Commission.

(b)    (i) Each document filed or to be filed pursuant to the Exchange Act and incorporated by reference in the Time of Sale Prospectus or the Prospectus complied or will comply when so filed in all material respects with the Exchange Act and the applicable rules and regulations of the Commission thereunder, (ii) the Registration Statement, when it became effective, did not contain, and as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (iii) the Registration Statement as of the date hereof does not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (iv) the Registration Statement and the Prospectus comply and, as amended or supplemented, if applicable, will comply in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder, (v) the Time of Sale Prospectus does not, and at the time of each sale of the Shares in connection with the offering when the Prospectus is not yet available to prospective purchasers and at the Closing Date (as defined in Section 5), the Time of Sale Prospectus, as then amended or supplemented by the Company, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, (vi) each broadly available road show, if any, when considered together with the Time of Sale Prospectus, does not contain

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any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading and (vii) the Prospectus does not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, except that the representations and warranties set forth in this paragraph do not apply to statements or omissions in the Registration Statement, the Time of Sale Prospectus or the Prospectus based upon information relating to any Underwriter furnished to the Company in writing by such Underwriter through you expressly for use therein.

(c)    The Company is not an “ineligible issuer” in connection with the offering pursuant to Rules 164, 405 and 433 under the Securities Act. Any free writing prospectus that the Company is required to file pursuant to Rule 433(d) under the Securities Act has been, or will be, filed with the Commission in accordance with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder. Each free writing prospectus that the Company has filed, or is required to file, pursuant to Rule 433(d) under the Securities Act or that was prepared by or on behalf of or used or referred to by the Company complies or will comply in all material respects with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder. Except for the free writing prospectuses, if any, identified in Schedule III hereto, and electronic road shows, if any, furnished to you before first use, the Company has not prepared, used or referred to, and will not, without your prior consent, prepare, use or refer to, any free writing prospectus.

(d)    The Company has been duly incorporated, is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and is duly qualified to transact business and is in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not have a material adverse effect on the Company and its subsidiaries, taken as a whole; each such jurisdiction is set forth on Schedule IV hereto.

(e)    Each “significant subsidiary” (within the meaning of Rule 1-02(w) of Regulation S-X under the Securities Act) of the Company has been duly incorporated, is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and is duly qualified to transact business and is in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing

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of property requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not have a material adverse effect on the Company and its subsidiaries, taken as a whole; all of the issued and outstanding shares of capital stock of each subsidiary of the Company have been duly and validly authorized and issued, are fully paid and non-assessable and are owned directly or indirectly by the Company, free and clear of all liens, encumbrances, equities or claims.

(f)    This Agreement has been duly authorized, executed and delivered by the Company.

(g)    The authorized capital stock of the Company conforms as to legal matters to the description thereof contained in each of the Time of Sale Prospectus and the Prospectus.

(h)    The shares of Common Stock (including the Shares to be sold by the Selling Shareholder) outstanding prior to the sale of the Shares to be sold by the Selling Shareholder have been duly authorized and are validly issued, fully paid and non-assessable.

(i)    The execution and delivery by the Company of, and the performance by the Company of its obligations under, this Agreement will not contravene any provision of applicable law or the certificate of incorporation or by-laws of the Company or any agreement or other instrument binding upon the Company or any of its subsidiaries that is material to the Company and its subsidiaries, taken as a whole, or any judgment, order or decree of any governmental body, agency or court having jurisdiction over the Company or any subsidiary, and no consent, approval, authorization or order of, or qualification with, any governmental body or agency is required for the performance by the Company of its obligations under this Agreement, except for those that have been obtained and such as may be required by the securities or Blue Sky laws of the various states in connection with the offer and sale of the Shares.

(j)    There has not occurred any material adverse change, or any development involving a prospective material adverse change, in the condition, financial or otherwise, or in the earnings, business or operations of the Company and its subsidiaries, taken as a whole, from that set forth in the Time of Sale Prospectus.

(k)    There are no legal or governmental proceedings pending or, to the knowledge of the Company, threatened to which the Company or any of its subsidiaries is a party or to which any of the properties of the Company or any of its subsidiaries is subject that are required to be described in the Registration Statement or the Prospectus and are not so described; and there are no statutes, regulations, contracts or other documents that are required to be described in the

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Registration Statement or the Prospectus or to be filed as exhibits to the Registration Statement that are not described or filed as required.

(l)    Each preliminary prospectus filed as part of the registration statement as originally filed or as part of any amendment thereto, or filed pursuant to Rule 424 under the Securities Act, complied when so filed in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder.

(m)    The Company is not, and after giving effect to the offering and sale of the Shares as described in the Prospectus will not be, required to register as an “investment company” as such term is defined in the Investment Company Act of 1940, as amended.

(n)    The Company and its subsidiaries (i) are in compliance with any and all applicable foreign, federal, state and local laws and regulations relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (“ Environmental Laws ”), (ii) have received all permits, licenses or other approvals required of them under applicable Environmental Laws to conduct their respective businesses and (iii) are in compliance with all terms and conditions of any such permit, license or approval, except where such noncompliance with Environmental Laws, failure to receive required permits, licenses or other approvals or failure to comply with the terms and conditions of such permits, licenses or approvals would not, singly or in the aggregate, have a material adverse effect on the Company and its subsidiaries, taken as a whole.

(o)    There are no costs or liabilities associated with Environmental Laws (including, without limitation, any capital or operating expenditures required for clean-up, closure of properties or compliance with Environmental Laws or any permit, license or approval, any related constraints on operating activities and any potential liabilities to third parties) which would, singly or in the aggregate, have a material adverse effect on the Company and its subsidiaries, taken as a whole.

(p)    Except as disclosed in the preliminary prospectus and Prospectus, there are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Securities Act with respect to any securities of the Company or to require the Company to include such securities with the Shares registered pursuant to the Registration Statement, other than rights that have been waived.

(q)    The Company and its subsidiaries own or possess, or license or have the right to use, or can acquire on reasonable terms, all material patents,

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patent rights, licenses, inventions, copyrights, know how (including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems or procedures), trademarks, service marks and trade names currently employed by them in connection with the business now operated by them, and neither the Company nor any of its subsidiaries has received any notice of infringement of or conflict with asserted rights of others with respect to any of the foregoing which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, would have a material adverse effect on the Company and its subsidiaries, taken as a whole.

(r)    The Company has received the consideration for the Shares specified in the Exchange and Recapitalization Agreement (the “Exchange Agreement”), dated as of May 10, 2006, by and among the Company and each of the investors set forth therein.

2.     Representations and Warranties of the Selling Shareholder . The Selling Shareholder represents and warrants to and agrees with each of the Underwriters that:

(a)    This Agreement has been duly authorized, executed and delivered by the Selling Shareholder.

(b)    The execution and delivery by the Selling Shareholder of, and the performance by the Selling Shareholder of its obligations under, this Agreement, will not contravene any provision of applicable law, or the certificate of incorporation or by-laws of the Selling Shareholder, or any agreement or other instrument binding upon the Selling Shareholder or any judgment, order or decree of any governmental body, agency or court having jurisdiction over the Selling Shareholder, and no consent, approval, authorization or order of, or qualification with, any governmental body or agency is required for the performance by the Selling Shareholder of its obligations under this Agreement, except such as may be required by the securities or Blue Sky laws of the various states in connection with the offer and sale of the Shares.

(c)    The Selling Shareholder has, and on the Closing Date will have, valid title to, or a valid “security entitlement” within the meaning of Section 8-501 of the New York Uniform Commercial Code in respect of, the Shares to be sold by the Selling Shareholder free and clear of all security interests, claims, liens, equities or other encumbrances and the legal right and power, and all authorization and approval required by law, to enter into this Agreement and to sell, transfer and deliver the Shares to be sold by the Selling Shareholder or a security entitlement in respect of such Shares.

(d)    Delivery of the Shares to be sold by the Selling Shareholder and payment therefor pursuant to this Agreement will pass valid title to the Shares,

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free and clear of any adverse claim within the meaning of Section 8-102 of the New York Uniform Commercial Code, to each Underwriter who has purchased such Shares without notice of an adverse claim.

(e)    (i) The Registration Statement, when it became effective, did not contain, as amended or supplemented, if applicable, and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (ii) the Registration Statement as of the date hereof does not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (iii) the Time of Sale Prospectus does not, and at the time of each sale of the Shares in connection with the offering when the Prospectus is not yet available to prospective purchasers and at the Closing Date (as defined in Section 5), the Time of Sale Prospectus, as then amended or supplemented by the Company, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, each broadly available road show, if any, when considered together with the Time of Sale Prospectus, does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading and the Prospectus does not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, provided that the representations and warranties set forth in this paragraph 2(e) are limited to statements or omissions made in reliance upon information relating to the Selling Shareholder furnished to the Company in writing by the Selling Shareholder expressly for use in the Registration Statement, the Prospectus or any amendments or supplements thereto.

3.     Agreements to Sell and Purchase . The Selling Shareholder hereby agrees to sell to the several Underwriters, and each Underwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Selling Shareholder at $37.1475 a share (the “ Purchase Price ”) the respective number of Shares opposite the name of such Underwriter on Schedule I hereto.

4.     Terms of Public Offering . The Company and the Selling Shareholder are advised by you that the Underwriters propose to make a public offering of their respective portions of the Shares as soon after the Registration Statement and this Agreement have become effective as in your judgment is advisable. The Company and the Selling Shareholder are further advised by you that the Shares are to be offered to the public initially at $39.00 a share (the “ Public Offering

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Price ”) and to certain dealers selected by you at a price that represents a concession not in excess of $0.9945 a share under the Public Offering Price.

5.     Payment and Delivery . Payment for the Shares to be sold by the Selling Shareholder shall be made to the Selling Shareholder in Federal or other funds immediately available in New York City against delivery of such Shares for the respective accounts of the several Underwriters at 10:00 a.m., New York City time, on January 23, 2007, or at such other time on the same or such other date, not later than January 24, 2007, as shall be designated in writing by you. The time and date of such payment are hereinafter referred to as the “ Closing Date .”

The Shares shall be registered in such names and in such denominations as you shall request in writing not later than one full business day prior to the Closing Date. The Shares shall be delivered to you on the Closing Date for the respective accounts of the several Underwriters, with any transfer taxes payable in connection with the transfer of the Shares to the Underwriters duly paid, against payment of the Purchase Price therefor.

6.     Conditions to the Underwriters’ Obligations . The obligations of the Selling Shareholder to sell the Shares to the Underwriters and the several obligations of the Underwriters to purchase and pay for the Shares on the Closing Date are subject to the condition that the Registration Statement shall have become effective prior to the date hereof.

The several obligations of the Underwriters are subject to the following further conditions:

(a)    Subsequent to the execution and delivery of this Agreement and prior to the Closing Date:

(i)    there shall not have occurred any downgrading, nor shall any notice have been given of any intended or potential downgrading or of any review for a possible change that does not indicate the direction of the possible change, in the rating accorded any of the securities of the Company or any of its subsidiaries by any “nationally recognized statistical rating organization,” as such term is defined for purposes of Rule 436(g)(2) under the Securities Act; and

(ii)    there shall not have occurred any change, or any development involving a prospective change, in the condition, financial or otherwise, or in the earnings, business or operations of the Company and its subsidiaries, taken as a whole, from that set forth in the Time of Sale Prospectus that, in your judgment, is material and adverse and that makes it, in your judgment, impracticable to market the Shares on the terms and in the manner contemplated in the Time of Sale Prospectus.

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(b)    The Underwriters shall have received on the Closing Date a certificate, dated the Closing Date and signed by the Chief Executive Officer or Chief Financial Officer of the Company, to the effect set forth in Section 6(a)(i) above and to the effect that the representations and warranties of the Company contained in this Agreement are true and correct as of the Closing Date and that the Company has complied with all of the agreements and satisfied all of the conditions on its part to be performed or satisfied hereunder on or before the Closing Date.

The officer signing and delivering such certificate may rely upon the best of his or her knowledge as to proceedings threatened.

(c)    The Underwriters shall have received on the Closing Date an opinion of Hogan & Hartson LLP, outside counsel for the Company, dated the Closing Date in the form attached as Exhibit B hereto, and an opinion of Meredith M. Todd, Associate General Counsel of the Company, dated the Closing Date in the form attached hereto as Exhibit C.

(d)    The Underwriters shall have received on the Closing Date an opinion of Latham & Watkins LLP, counsel for the Selling Shareholder, dated the Closing Date in the form attached hereto as Exhibit D.

(e)    The Underwriters shall have received on the Closing Date an opinion of Davis Polk & Wardwell, counsel for the Underwriters, dated the Closing Date, in form and substance reasonably satisfactory to the Underwriters.

The opinions of Hogan & Hartson LLP, the Associate General Counsel of the Company and Latham & Watkins LLP described in Sections 6(c) and 6(d) above shall be rendered to the Underwriters at the request of the Company or the Selling Shareholder, as the case may be, and shall so state therein.

(f)    The Underwriters shall have received, on each of the date hereof and the Closing Date, a letter dated the date hereof or the Closing Date, as the case may be, in form and substance satisfactory to the Underwriters, from Ernst & Young LLP, independent public accountants, containing statements and information of the type ordinarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained in or incorporated by reference into the Registration Statement, the Time of Sale Prospectus and the Prospectus; provided that the letter delivered on the Closing Date shall use a “cut-off date” not earlier than the date hereof.

(g)    The “lock-up” agreements, each substantially in the form of Exhibit A hereto, between you and the stockholders of the Company listed on Schedule II hereto and the officers and directors of the Company relating to sales and certain other dispositions of shares of Common Stock or certain other

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securities, delivered to you on or before the date hereof, shall be in full force and effect on the Closing Date.

7.     Covenants of the Company . The Company covenants with each Underwriter as follows:

(a)    To furnish to you, without charge, three signed copies of the Registration Statement (including exhibits thereto and documents incorporated by reference therein) and for delivery to each other Underwriter a conformed copy of the Registration Statement (without exhibits thereto but including documents incorporated by reference therein) and to furnish to you in New York City, without charge, prior to 10:00 a.m. New York City time on the business day next succeeding the date of this Agreement and during the period mentioned in Section 7(e) or 7(f) below, as many copies of the Time of Sale Prospectus, the Prospectus and any documents incorporated therein by reference and any supplements and amendments thereto or to the Registration Statement as you may reasonably request.

(b)    Before amending or supplementing the Registration Statement, the Time of Sale Prospectus or the Prospectus, to furnish to you a copy of each such proposed amendment or supplement and not to file any such proposed amendment or supplement to which you reasonably object, and to file with the Commission within the applicable period specified in Rule 424(b) under the Securities Act any prospectus required to be filed pursuant to such Rule.

(c)    To furnish to you a copy of each proposed free writing prospectus to be prepared by or on behalf of, used by, or referred to by the Company and not to use or refer to any proposed free writing prospectus to which you reasonably object.

(d)    Not to take any action that would result in an Underwriter or the Company being required to file with the Commission pursuant to Rule 433(d) under the Securities Act a free writing prospectus prepared by or on behalf of the Underwriter that the Underwriter otherwise would not have been required to file thereunder.

(e)    If the Time of Sale Prospectus is being used to solicit offers to buy the Shares at a time when the Prospectus is not yet available to prospective purchasers and any event shall occur or condition exist as a result of which it is necessary to amend or supplement the Time of Sale Prospectus in order to make the statements therein, in the light of the circumstances, not misleading, or if any event shall occur or condition exist as a result of which the Time of Sale Prospectus conflicts with the information contained in the Registration Statement then on file, or if, in the opinion of counsel for the Underwriters, it is necessary to amend or supplement the Time of Sale Prospectus to comply with applicable law,

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forthwith to prepare, file with the Commission and furnish, at its own expense, to the Underwriters and to any dealer upon request, either amendments or supplements to the Time of Sale Prospectus so that the statements in the Time of Sale Prospectus as so amended or supplemented will not, in the light of the circumstances when delivered to a prospective purchaser, be misleading or so that the Time of Sale Prospectus, as amended or supplemented, will no longer conflict with the Registration Statement, or so that the Time of Sale Prospectus, as amended or supplemented, will comply with applicable law.

(f)    If, during such period after the first date of the public offering of the Shares as in the opinion of counsel for the Underwriters the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is required by law to be delivered in connection with sales by an Underwriter or dealer, any event shall occur or condition exist as a result of which it is necessary to amend or supplement the Prospectus in order to make the statements therein, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is delivered to a purchaser, not misleading, or if, in the opinion of counsel for the Underwriters, it is necessary to amend or supplement the Prospectus to comply with applicable law, forthwith to prepare, file with the Commission and furnish, at its own expense, to the Underwriters and to the dealers (whose names and addresses you will furnish to the Company) to which Shares may have been sold by you on behalf of the Underwriters and to any other dealers upon request, either amendments or supplements to the Prospectus so that the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is delivered to a purchaser, be misleading or so that the Prospectus, as amended or supplemented, will comply with law.

(g)    To endeavor to qualify the Shares for offer and sale under the securities or Blue Sky laws of such jurisdictions as you shall reasonably request.

(h)    To make generally available to the Company’s security holders a