Private equity has grown exponentially: it now controls and operates a large number of the companies in our economy. But private equity is just that: private. Its operations are confidential and difficult to parse. This article attempts to demystify the business of private equity. It also describes the unanimous decision by the 1st Circuit that a private equity fund is a trade or business for purposes of ERISA. Finally, the article discusses the tax implications of "trade or business" status for private equity funds and recommends further guidance from Treasury.