Johann Adolf Hasse (1699-1783) is one of the most outstanding composers of Italian opera seria of the mid-18th century. Between 1721 and 1771, Hasse composed over 50 opere serie; he also revised several of these operas more or less thoroughly for later performances. This volume focuses on 25 operas from the years 1730 to 1745. The first part recapitulates the life of the composer, in particular with a view to his career as an opera composer. It also sheds light on the source material and various facets of a widespread phenomenon in the 18th century of pre-existing material being used to revise operas or compose new ones. The author also examines the alterations made to Hasse's operas for later performances without his involvement. The second part of the book provides a comprehensive documentation of the works, the source material and verifiable performances in the 18th century. German text.