The Optimist is a small, single-crew sailing dinghy for children up to the age of 15. Nowadays boats are usually made of fiber reinforced plastic, although wooden boats are still built.

It is one of the most popular sailing dinghies in the world, with over 140,000 boats officially registered with the class and many more built but never registered.

The Optimist is also recognized as an International Class by the
International Sailing Federation.

Optimists are among the only boats well-suited for complete beginners to intermediate sailors between the ages of 7 and 15, with a weight range of 30-55kg. Very small children are sometimes "doubled up" in Optimists but in general the boats should be regarded as single-handers - it is in this mode that children gain the most in terms of confidence and improved skills. Most sailing schools have a number of them and they are the first boat most beginners will sail.

First-timer classes offered teach the rudiments of sailing technique in a variety of conditions depending on regional weather patterns but many also offer immediate immersion into competition within the topography of a standard race course.

Optimists are also the main training ground for future Olympic sailors. Over 60% start in the boat and over 40% of them are already international competitors by the age of 13-15. By December of the year in which they turn 15, Optimist racers are said to "age out"; that is, they become too old to continue racing.

The Optimist is the biggest and most competitive youth racing class in the world. As well as the annual world championship the class also has six continental championships, attended by a total of over 700 sailors a year. Many thousands more take part in international and national regattas. Many of the top world Optimist sailors immediately become world-class Laser Radial or 4.7 sailors after they "age-out", and even average Optimist racers later do well in the "more advanced" classes including double-handers such as the 420 and 29er. Optimists provide real international competition because they are manufactured to the same specification by dozens of builders.

Over 4,000 boats a year are produced by nearly 40 builders worldwide.