Hermann of Reichenau (also called Hermannus Contractus or Hermannus Augiensis) (1013 July 18 – 1054 September 24) was an 11th century scholar, composer, music theorist, mathematician, and astronomer. Hermannus was a son of the duke of Altshausen. He was crippled by a paralytic disease from early childhood. He spent most of his life in the abbey of Reichenau, an island on Lake Constance. Hermannus contributed to all four arts of the quadrivium. He was renowned as a musical composer (among his surviving works are officia for St. Afra and St. Wolfgang). He also wrote a treatise on the science of music, several works on geometry and arithmetics and astronomical treatises (including instructions for the construction of an astrolabe, at the time a very novel device in Christian Europe). As a historian, he wrote a detailed chronicle from the birth of Christ to his own present day, for the first time compiling the events of the 1st millennium AD scattered in various chronicles in a single work, ordering them after the reckoning of the Christian era. His disciple Berthold of Reichenau was its continuator.

He was beatified (cultus confirmed) in 1863.