In 1964 in Helsinki, the World Medical Association (WMA) first adopted a set of guidelines on ethical principles for medical research involving human subjects, known as the Declaration of Helsinki, which has been amended several times since then. The last amendment was ratified in October 2013 at the 64th Annual General Meeting in Fortaleza, Brazil. While it is not a legally binding set of rules, laws around the world refer to different versions of the Declaration. In Germany, it is referred to in the professional code of conduct for physicians of the German Medical Association.