The sound and visual diversity of the organ is unmatched by any other musical instrument. Just as its history is varied, so too is the perception of this complex machinery. Michael Praetorius referred to it in 1619 as the 'instrument of instruments,' while György Ligeti in the 20th century described it as a 'huge prosthesis,' emphasizing the challenge of learning to 'walk anew' with it. Now, for the first time, a reference work is dedicated to the phenomenon of the organ, providing concentrated information on all essential aspects of the instrument and its music. The Encyclopedia of the Organ connects representations of the works of composers and organ builders, performers, and scholars with articles on organ construction, organ music, and organ playing. The focus is not only on the church instrument and its music but also on the predecessors and secular offshoots of organ development.