The Leahy-Smith America Invents Act is a United States federal statute passed by Congress and signed into law by President Barack Obama on September 16, 2011. The law represents the most significant legislative change to the U.S. patent system since the Patent Act of 1952 and closely resembles previously proposed legislation in the Senate with the Patent Reform Act of 2009. 

Named for its lead sponsors, Sen. Patrick Leahy (DVT) and Rep. Lamar Smith (RTX), the Act switches the U.S. patent system from a “first to invent” to a “first inventor to file” system, eliminates interference proceedings and develops post-grant opposition. Its central provisions went into effect on September 16, 2012 and on March 16, 2013.