Mannheim school refers to both the orchestral techniques pioneered by the court orchestra of Mannheim in the latter half of the 18th century as well as the group of composers who wrote such music for the orchestra of Mannheim and others.
The court of the Elector Carl Philipp moved from Heidelberg to Mannheim in 1720, already employing an orchestra larger than that of any of the surrounding states. This grew even further in the following decades and came to include some of the best virtuosi of the time. It was joined by Johann Stamitz, who is generally considered to be the founder of the Mannheim school, in 1741/42, and he became its director in 1750.
The most notable of the revolutionary techniques of the Mannheim orchestra were its more independent treatment of the wind instruments and its famous whole-orchestra crescendo, a stark contrast to the dynamics of baroque music, which allowed only for instantaneous changes from forte to piano and back.
Members of the Mannheim school included Johann Stamitz, Franz Xaver Richter, Carl Stamitz and Christian Cannabich, and it had a very direct influence on many major symphonists of the time, including Joseph Haydn and Leopold Hofmann. Cannabich, one of the directors of the orchestra after the death of J. Stamitz, was also a good friend of Wolfgang Amadeus Mozart from the latter's visit to Mannheim in 1777 onwards.