In 1997, the Government of Australia took the unprecedented step of capping water abstractions from the Murray-Darling River Basin at 1993/94 levels, in an effort to preserve and restore this vital but overconsumed resource. The Cap helped to establish a formal market for freshwater entitlements, in which irrigators can buy and sell the right to pump water out of the Murry-Darling River Basin. Since the program's introduction, audits have shown the Cap to be highly successful in protecting the health and flow of the River Basin. This brochure, put together by Australia's Murray-Darling River Basin Commission, introduces why and how the Cap was put into effect, as well as its effects to date.