A positive organ (also positiv organ, positif organ, portable organ, chair organ, or simply positive, positiv, positif, or chair) (from the Latin verb ponere, "to place") is a small, usually one-manual, pipe organ that is built to be more or less mobile. It was common in sacred and secular music between the 10th and the 18th centuries, in chapels and small churches, as a chamber organ and for the basso continuo in ensemble works. The smallest common kind of positive, hardly higher than the keyboard, is called chest or box organ and is especially popular nowadays for basso continuo work; positives for more independent use tend to be higher.

From the Middle Ages through Renaissance and Baroque the instrument came in many different forms, including processional and tabletop organs that have profited relatively less from the renewed popularity the type in general has enjoyed from the Orgelbewegung onwards.