The Argentinean Congreso de la Nacion (National Congress, or Parliament) approved in November 2010 a new Mental Health Law (MHL) (Law 26657, ‘Salud Publico. Derecho a la Proteccion de la Salud Mental’ [Public Health. The Right to Protect Mental Health]). Although it is not the first law concerning mental health – as several of the provinces and the autonomous city of Buenos Aires (Argentina's capital) have enacted their own – the MHL establishes principles for human rights and the protection of patients, and aims to develop approaches in mental health that are compatible with the most advanced views and legislation from high-income countries. In this paper we report on the most important aspects of the MHL. We highlight areas that represent a change for Argentina, such as the new arrangements for both informal and compulsory admission to hospital.