| 21. | Orchestra musicians (5) |
| 22. | Orchestra musicians--Training (6) |
| 23. | Orchestras (59) |
| 24. | Orchestras, youth (13) |
| 25. | Orchestre (10) |
| 26. | Orchestres (59) |
| 27. | Orchestres de danse (7) |
| 28. | Orchestres de jeunes (13) |
| 29. | Organ (44) |
| 30. | Organ music--History (3) |
| 31. | Organ--Building and builders (15) |
| 32. | Organ--Composition for (8) |
| 33. | Organisation de concerts (10) |
| 34. | Organistes (10) |
| 35. | Organists (10) |
| 36. | Organ--Italy (1) |
| 37. | Organs, pipe (20) |
| 38. | Organs, theatre (1) |
| 39. | Orgue (44) |
| 40. | Orgue--Composition pour (8) |