1


                                                                     Exhibit 5.1



                                HALE AND DORR LLP
                       60 STATE STREET - BOSTON, MA 02109
                         617-526-6000 - FAX 617-526-5000


                                                   June 1, 2001




Akamai Technologies, Inc.
500 Technology Square
Cambridge, Massachusetts 02139

         1999 Employee Stock Purchase Plan
         Second Amended and Restated 1998 Stock Incentive Plan
         -----------------------------------------------------

Ladies and Gentlemen:

         We have assisted in the preparation of a Registration Statement on Form
S-8 (the "Registration Statement") to be filed with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), relating to an aggregate of 6,000,000 shares of common stock,
$0.01 par value per share (the "Shares"), of Akamai Technologies, Inc., a
Delaware corporation (the "Company"), issuable under the Company's Second
Amended and Restated 1998 Stock Incentive Plan and 1999 Employee Stock Purchase
Plan (collectively, the "Plans").

         We have examined the Certificate of Incorporation and By-Laws of the
Company, each as amended and restated to date, and originals, or copies
certified to our satisfaction, of all pertinent records of the meetings of the
directors and stockholders of the Company, the Registration Statement and such
other documents relating to the Company as we have deemed material for the
purposes of this opinion.

         In our examination of the foregoing documents, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals, the conformity to original documents of all documents submitted to
us as certified, photostatic or other copies, the authenticity of the originals
of any such documents and the legal competence of all signatories to such
documents.

         We assume that the appropriate action will be taken, prior to the offer
and sale of the shares in accordance with the Plans, to register and qualify the
shares for sale under all applicable state securities or "blue sky" laws.

         We express no opinion herein as to the laws of any state or
jurisdiction other than the state laws of The Commonwealth of Massachusetts, the
General Corporation Law of the State of Delaware and the federal laws of the
United States of America.

   2

         It is understood that this opinion is to be used only in connection
with the offer and sale of the Shares while the Registration Statement is in
effect.

         Please note that we are opining only as to the matters expressly set
forth herein, and no opinion should be inferred as to any other matters.

         Based on the foregoing, we are of the opinion that the Shares have been
duly authorized for issuance and, when the Shares are issued and paid for in
accordance with the terms and conditions of the Plans, the Shares will be
validly issued, fully paid and nonassessable.

         We hereby consent to the filing of this opinion with the Securities and
Exchange Commission in connection with the Registration Statement in accordance
with the requirements of Item 601(b)(5) of Regulation S-K under the Securities
Act. In giving such consent, we do not hereby admit that we are in the category
of persons whose consent is required under Section 7 of the Securities Act or
the rules and regulations of the Commission.


                                              Very truly yours,

                                              /S/ HALE AND DORR LLP
                                              ---------------------
                                              HALE AND DORR LLP