An amphibian aircraft or amphibious aircraft can land on land, or water, but there are great penalties involved: The aircraft will have to handle the extra drag, and weight, of the hull-shaped fuselage, or the floats (see seaplane), and the associated hardware, plus the weight of the landing gear (which normally is retractable, or, on smaller aicraft, semi-retractable). This leads in turn to the use of bigger, more powerful, engine(s) than comparable land aircraft, which in turn escalates weights and/or reduces range.

The amphibian aircraft have their uses, not least as transport aircraft in remote areas, where there are few airstrips, but plenty of lakes and rivers. And they are more versatile than normal seaplanes and flying boats, as they can be flown to a big airport, or airfield, to get service, or just to be able to land, or take-off, when a storm makes the waves too big to handle.

By necessity, amphibian aircraft are heavy, complex and expensive to buy and run, but very versatile. And yet, on the whole, cheaper to buy and operate, and simpler, than the helicopters that compete for the same types of jobs, if not quite as versatile. Amphibious aircraft have longer range than a comparable helicopter, as an aircraft's wing is more effective than a helicopter's lifting rotor.

Almost no flying boats are manufactured today, but numerous land aircraft are each year converted to amphibious seaplane configuration by exchanging their fixed landing gear for amphibious floats. A handfull manufactures around the world still manufactures amphibian aircraft (flying boats with retractable landing gear), but their numbers are dwindling.