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                                                                     Exhibit 5.1







                      [LETTERHEAD OF WINSTON & STRAWN LLP]





                                December 8, 2006


IPG Photonics Corporation
50 Old Webster Road
Oxford, Massachusetts 01540

              Re:    Form S-1 Registration Statement (Registration No.
                     333-136521)

Ladies and Gentlemen:


              We have acted as counsel for IPG Photonics Corporation, a Delaware
corporation (the "Company"), in connection with the preparation and filing of
its Registration Statement on Form S-1 (Registration No. 333-136521) initially
filed with the Securities and Exchange Commission (the "Commission") on August
11, 2006 (as amended through the date hereof, the "Registration Statement"),
under the Securities Act of 1933, as amended (the "Securities Act"). The
Registration Statement relates to the registration of the offer and sale by the
Company and certain selling stockholders (the "Offering") of up to 10,350,000
shares (the "Shares") of common stock, par value $0.0001 per share (the "Common
Stock"), including (i) 6,241,379 shares (the "Primary Shares") of Common Stock
that may be offered by the Company pursuant to the Registration Statement, (ii)
2,758,621 shares of Common Stock that may be offered by certain selling
stockholders pursuant to the Registration Statement and (iii) 1,350,000 shares
of Common Stock that may be offered by certain selling stockholders to cover
over-allotments pursuant to the Registration Statement (the Shares described in
subclauses (ii) and (iii) being herein referred to as the "Secondary Shares").

              This opinion letter is being furnished in accordance with the
requirements of Item 601(b)(5) of Regulation S-K under the Securities Act.

              In rendering the opinion set forth below, we have examined and
relied upon such certificates, corporate records, agreements, instruments and
other documents that we considered necessary or appropriate as a basis for the
opinion, including (i) the Registration Statement, (ii) the Amended and Restated
Certificate of Incorporation of the Company, as amended, (iii) the second
Amended and Restated Certificate of Incorporation of the Company and (iv) the
Amended and Restated By-laws of the Company. In our examination, we have assumed
the


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IPG Photonics Corporation
December 8, 2006
Page 2


legal capacity of all natural persons, the genuineness of all signatures, the
authenticity of all documents submitted to us as certified or photostatic copies
and the authenticity of the originals of such latter documents. As to any facts
material to this opinion that we did not independently establish or verify, we
have relied upon oral or written statements and representations of officers and
other representatives of the Company and others.

              Based upon the foregoing and subject to the assumptions,
qualifications and limitations set forth herein, we are of the opinion that (1)
the Primary Shares have been duly authorized by all requisite corporate action
on the part of the Company and, when duly delivered against payment therefor as
contemplated by the Underwriting Agreement the form of which has been filed as
Exhibit 1.1 to the Registration Statement, will be validly issued, fully paid
and nonassessable and (2) the Secondary Shares have been duly authorized by all
requisite corporate action on the part of the Company and are validly issued,
fully paid and nonassessable.

              The foregoing opinion is limited to the General Corporation Law of
the State of Delaware, including the statutory provisions, the applicable
provisions of the Delaware Constitution and reported judicial decisions
interpreting the foregoing. We express no opinion with respect to any other
laws, statutes, regulations or ordinances.

              We hereby consent to the filing of this opinion as Exhibit 5.1 to
the Registration Statement and to the reference to our firm under the caption
"Legal Matters" in the Prospectus included in the Registration Statement. In
giving such consent, we do not concede that we are experts within the meaning of
the Securities Act or the rules and regulations thereunder or that this consent
is required by Section 7 of the Securities Act.

                                        Very truly yours,


                                        /s/   Winston & Strawn LLP
