Seaplanes are a class of fixed-wing aircraft which are designed to take off and alight on water. In some parts of the world, the aircraft are referred to as hydroplanes. There are a number of different styles of seaplane designed for an assortment of uses. Although seaplanes are not as common as they were during their heyday in the 1920s and 1930s, the aircraft are still in use in some areas of the world. Seaplanes are especially popular in areas with lots of lakes and rivers, such as Canada, since they can use a body of water as a runway, making access in rural areas very convenient.

There are two basic styles of seaplane. In the first, floats are installed below the fuselage of the plane, allowing it to touch down on water and skim along it, almost as though the plane is on large water skis. The second design combines the float and the fuselage of the aircraft, making a flying boat which may also have floats on its wings for additional buoyancy. Many people think of float planes when they visualize seaplanes, since the planes look so distinctive.

Seaplanes can also be amphibious, in which case they are usually referred to specifically as amphibious aircraft. An amphibious seaplane has retractable wheels allowing it to navigate on land as well as on the water. Many amphibious seaplanes are flying boats, since the floats can make take off and landing on land awkward. The Grumman Goose is a well known historical example of an amphibious seaplane.

The first seaplanes appeared in the early 1900s, and commercial flights on seaplanes were available by the 1930s. In the Second World War, many militaries used seaplanes, and they continue to be utilized for this purpose. Most modern seaplanes are small private aircraft, rather than commercial planes, designed for light duty around lakes and harbors. Some charter services keep a fleet of seaplanes for traveling to remote regions.

Rescue services may also keep a seaplane on hand, as the aircraft can identify and retrieve victims in the water. In areas with extremely cold water, this can be very valuable, as victims can be rescued as soon as they are spotted, rather than having to wait for help to arrive on site. This rapid rescue makes a complete recovery from exposure more probable.

Just like other aircraft, seaplanes can struggle in bad weather. They also have difficulty landing on turbulent waters, which can be problematic. Most seaplanes are given ratings which indicate which kind of weather conditions they can land in, with larger aircraft being more able to handle heavy wave action.