The organ builder for any building is the company, workshop, or craftsman who designs and constructs a musical organ, usually a pipe organ which is permanently installed in that building. This is most frequently applied to religious buildings like churches, but is not uncommon in theaters, opera houses, and other show venues.

The organ is the musical instrument designed and built by the company, workshop, or individual craftsman. A permanently installed pipe organ is the usual example, rather than a requirement that the maker be a large manufacturing company.

The building can be a place of worship or a performance venue. Its religious or theatrical use does not change the instrument-building activity, and the organ builder is distinct from the person who performs on the completed instrument.