While state law recognizes an LLC as a distinct type of entity, an LLC is not a distinct entity for federal tax purposes. An LLC that has two or more owners is treated as either a corporation or a partnership, while an LLC with a single owner will be disregarded for federal income tax purposes unless it elects to be treated as a corporation. In addition to single-member LLCs, the Code and Regulations recognize a second type of disregarded entity – the qualified subchapter S subsidiary (commonly called a QSub). The first part of this Article examines the tax consequences of (1) the formation and dissolution of single member LLCs, (2) check-the-box elections and revocations for a single member LLC, (3) the addition of a second member to an LLC, which converts a disregarded entity into a partnership, (4) the reduction of the number of members of an LLC from two or more to one, which converts the LLC from a partnership into a disregarded entity, (5) the election by a LLC to be taxed as a corporation – including “check and sell” and “check and merge” transactions – and the revocation of an election by an LLC to be taxed as a corporation, (6) the merger of a single member LLC into another LLC or a partnership, and (7) the merger of an LLC into a corporation. The second part of the Article examines the treatment of QSub elections, revocations, and terminations, in various contexts, including merger and acquisition transactions.