26 U.S.C. § 2501 : US Code - Section 2501: Imposition of tax

    (a) Taxable transfers
      (1) General rule
        A tax, computed as provided in section 2502, is hereby imposed
      for each calendar year on the transfer of property by gift during
      such calendar year by any individual resident or nonresident.
      (2) Transfers of intangible property
        Except as provided in paragraph (3), paragraph (1) shall not
      apply to the transfer of intangible property by a nonresident not
      a citizen of the United States.
      (3) Exception
        (A) Certain individuals
          Paragraph (2) shall not apply in the case of a donor to whom
        section 877(b) applies for the taxable year which includes the
        date of the transfer.
        (B) Credit for foreign gift taxes
          The tax imposed by this section solely by reason of this
        paragraph shall be credited with the amount of any gift tax
        actually paid to any foreign country in respect of any gift
        which is taxable under this section solely by reason of this
        paragraph.
      (4) Transfers to political organizations
        Paragraph (1) shall not apply to the transfer of money or other
      property to a political organization (within the meaning of
      section 527(e)(1)) for the use of such organization.
      (5) Transfers of certain stock
        (A) In general
          In the case of a transfer of stock in a foreign corporation
        described in subparagraph (B) by a donor to whom section 877(b)
        applies for the taxable year which includes the date of the
        transfer - 
            (i) section 2511(a) shall be applied without regard to
          whether such stock is situated within the United States, and
            (ii) the value of such stock for purposes of this chapter
          shall be its U.S.-asset value determined under subparagraph
          (C).
        (B) Foreign corporation described
          A foreign corporation is described in this subparagraph with
        respect to a donor if - 
            (i) the donor owned (within the meaning of section 958(a))
          at the time of such transfer 10 percent or more of the total
          combined voting power of all classes of stock entitled to
          vote of the foreign corporation, and
            (ii) such donor owned (within the meaning of section
          958(a)), or is considered to have owned (by applying the
          ownership rules of section 958(b)), at the time of such
          transfer, more than 50 percent of - 
              (I) the total combined voting power of all classes of
            stock entitled to vote of such corporation, or
              (II) the total value of the stock of such corporation.
        (C) U.S.-asset value
          For purposes of subparagraph (A), the U.S.-asset value of
        stock shall be the amount which bears the same ratio to the
        fair market value of such stock at the time of transfer as - 
            (i) the fair market value (at such time) of the assets
          owned by such foreign corporation and situated in the United
          States, bears to
            (ii) the total fair market value (at such time) of all
          assets owned by such foreign corporation.
    (b) Certain residents of possessions considered citizens of the
      United States
      A donor who is a citizen of the United States and a resident of a
    possession thereof shall, for purposes of the tax imposed by this
    chapter, be considered a "citizen" of the United States within the
    meaning of that term wherever used in this title unless he acquired
    his United States citizenship solely by reason of (1) his being a
    citizen of such possession of the United States, or (2) his birth
    or residence within such possession of the United States.
    (c) Certain residents of possessions considered nonresidents not
      citizens of the United States
      A donor who is a citizen of the United States and a resident of a
    possession thereof shall, for purposes of the tax imposed by this
    chapter, be considered a "nonresident not a citizen of the United
    States" within the meaning of that term wherever used in this
    title, but only if such donor acquired his United States
    citizenship solely by reason of (1) his being a citizen of such
    possession of the United States, or (2) his birth or residence
    within such possession of the United States.
    (d) Cross references
          (1) For increase in basis of property acquired by gift for
        gift tax paid, see section 1015(d).
          (2) For exclusion of transfers of property outside the United
        States by a nonresident who is not a citizen of the United
        States, see section 2511(a).