Introduction Investments that yield tax benefits are sometimes called "tax shelters." In some cases, Congress has concluded that the loss of revenue is an acceptable side effect of special tax provisions designed to encourage taxpayers to make certain types of investments. In many cases, however, losses from tax shelters produce little or no benefit to society, or the tax benefits are exaggerated beyond those intended. Those cases are called "abusive tax shelters." An investment that is considered a tax shelter is subject to restrictions, including the requirement that it be registered, as discussed later, unless it is a projected income investment (defined later).