Part of a comparative survey on tax treatment of index participation units (IPUs) in Argentina and the USA. This part describes the US index participation shares (IPSs) as they briefly existed along with tax and accounting principles as they might apply to this type of instrument. The article then discusses exchange-traded funds (ETFs) and their treatment under US tax law. Finally, the article points out the ways in which the US tax treatment of the derivative instrument (IPSs) differs from that of the actual ownership interests (ETFs).