26 CFR § 1.318-1 - Constructive ownership of stock; introduction.
(a) For the purposes of certain provisions of chapter 1 of the Code, section 318(a) provides that stock owned by a taxpayer includes stock constructively owned by such taxpayer under the rules set forth in such section. An individual is considered to own the stock owned, directly or indirectly, by or for his spouse (other than a spouse who is legally separated from the individual under a decree of divorce or separate maintenance), and by or for his children, grandchildren, and parents. Under section 318(a)(2) and (3), constructive ownership rules are established for partnerships and partners, estates and beneficiaries, trusts and beneficiaries, and corporations and stockholders. If any person has an option to acquire stock, such stock is considered as owned by such person. The term option includes an option to acquire such an option and each of a series of such options.
(b) In applying section 318(a) to determine the stock ownership of any person for any one purpose—
(1) A corporation shall not be considered to own its own stock by reason of section 318(a)(3)(C);
(2) In any case in which an amount of stock owned by any person may be included in the computation more than one time, such stock shall be included only once, in the manner in which it will impute to the person concerned the largest total stock ownership; and
(3) In determining the 50-percent requirement of section 318(a)(2)(C) and (3)(C), all of the stock owned actually and constructively by the person concerned shall be aggregated.