What is the name of the German beer purity law?

Reinheitsgebot Is a law from Germany put on the books years ago stating that only four ingredients may be used when brewing beer, these are barley, yeast, hops, and water. No other ingredients were permitted to be used when brewing beer. A German saying loosely translated as ‘Hops and malt for beer, may God preserve them here’ alludes to the basic ingredients used in beer brewing. These ingredients were laid down in the so-called ‘purity law’ in the Bavarian city of Ingolstadt in 1516. The purity law requires that ‘nothing other than barley, hops and water be used’ to produce beer. The importance of yeast was not known at the time and was added later. The purity law initially applied to the Duchy of Bavaria only but was gradually adopted by the German states and has been the law governing beer brewing in all of Germany since 1906.

In the past the law was upheld traditionally, but more recently it is not followed as closely.