One of the most hotly contested aspects of immigration reform is the proposal to give legal status to undocumented immigrants. Done properly, however, this should be a clear gain to productivity for the American economy, and for the economy of New York State.The key to achieving these productivity gains is dramatically reducing the number of undocumented immigrants. Legalization by itself will not be enough. In addition, there must be enforcement that prevents people from working without authorization, and legal channels for future immigration. This paper assumes that legalization would be accompanied by measures of this kind.