Triton is the largest moon of the planet Neptune, discovered on October 10, 1846 by William Lassell. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. At 2700 km in diameter, it is the seventh-largest moon in the Solar System. Triton comprises more than 99.5% of all the mass known to orbit Neptune, including the planet's rings and twelve other known moons.

Nereid was discovered on May 1, 1949 by Gerard P. Kuiper, who proposed the name in the report of his discovery. It is named after the Nereids, sea-nymphs of Greek mythology.

Nereid was the outermost known moon of Neptune from its discovery until 2002. Nereid's diameter is 340 km, making it the third-largest moon in the Neptune system. Its orbit averages 5,513,400 km in radius, but is highly eccentric and varies from 1,372,000 to 9,655,000 kilometres. This is the highest mean eccentricity of any known satellite in the solar system. But it may lose this title briefly to an outer irregular moon of a gas giant, such as Saturn's Bestla and Uranus's Margaret, because of the Kozai mechanism (a periodic exchange between the inclination and eccentricity). The unusual orbit suggests that it may be a captured asteroid or Kuiper belt object, or that it was perturbed during the capture of Neptune's largest moon Triton.

Despina is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter.

Despina was discovered in late July, 1989 from the images taken by the Voyager 2 probe. It was given the temporary designation S/1989 N 3. The discovery was announced (IAUC 4824) on August 2, 1989, but the text only talks of "10 frames taken over 5 days", giving a discovery date of sometime before July 28. The name was given on 16 September 1991.

Thalassa is the second innermost satellite of Neptune. Thalassa was named after a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea".