A reed organ is an organ that generates its sounds using similar free metal reeds to a piano accordion. Smaller, cheaper and more portable than the corresponding pipe instrument, these were widely used in smaller churches and in private homes, but their volume and tonal range was extremely limited, and they were generally limited to one or two manuals, pedalboards being extremely rare.

They have been largely replaced by electronic organs, but there remain a number of enthusiasts. The finer instruments have a unique tone, and the cabinets of those intended for churches were often excellent pieces of furniture.

A small reed organ with a manual or pedal operated blower worked by the player is called a harmonium. The harmonium is unique among organs in that expression can be added to the music by the way the player operates the blower, pedalling faster in louder passages for example.