| M6–M14 | Organ alone: |
| M6 | Collections, mixed (original works and arrangements; more than one composer) |
| M7 | General collections (one composer) |
| M8 | Sonatas |
| M8.5 | Symphonies |
| M9 | Suites, Variations, and Cyclical Works |
| M10 | Fugues (with or without preludes) |
| M11 | Pieces |
| M11.2 | Pedal pieces |
| M12 | Arrangements: collections |
| M13 | Arrangements: separate works |
| M14 | Books (accompaniments to collections of psalms and hymns) |
| M14.3-.5 | Liturgical music (special seasons and occasions) |
| M14.8 | Electronic Organ music |
| M180-186 | Duets |
| M180-181 | One or more organs, two or more players |
| M182-186 | Organ and one other instrument |
| M300–M304 | Trios, organ and two other instruments |
| M400–M404 | Quartets, organ and three other instruments |
Concertos and similar pieces
| M1005 | Organ with orchestra, full scores |
| M1005.5 | Cadenzas for such works |
| M1006 | Organ with orchestra, piano reductions |
| M1108 | Organ with string orchestra, full scores |
| M1108.5 | Cadenzas for such works |
| M1109 | Organ with string orchestra, piano reductions |
Studies and methods
| MT180 | General works |
| MT182 | Systems and methods; Studies and exercises |
| MT185 | General works: special techniques |
| MT187 | Special techniques: pedal |
| MT189 | Special techniques: registration |
| MT190 | Special techniques: accompaniment of liturgical music |
| MT193 | Teaching pieces; Instructive editions |
| MT198 | Self-instructors |
Classification Numbers for Books about the Organ
| ML128 .O6 | Organ bibliographies |
| ML550 | General works |
| ML552-597 | Construction: general works; by time period; by region or country; individual instruments; special parts |
| ML600-649 | Music and playing: general works; by time period; by region or country; forms and types of music |
