The "Beer Purity Law," known as the Reinheitsgebot, is a regulation that originated in Germany in 1516. It originally stated that beer could only be made from three ingredients: water, barley, and hops. This law aimed to ensure the quality and safety of beer, preventing the use of harmful additives. Over the years, the law has evolved, allowing for the inclusion of yeast as a fourth ingredient after its discovery. Today, the Reinheitsgebot is celebrated as a symbol of traditional brewing practices and is still influential in the production of German beer.