It is bordered (clockwise from north) by Vulpecula, Sagitta, Aquila, Aquarius, Equuleus and Pegasus.

According to myth, the first Greek god Poseidon wanted to marry Amphitrite, a beautiful nereid.

[2] The second story tells of the Greek poet Arion of Lesbos (7th century BC), who was saved by a dolphin.

[5] In Chinese astronomy, the stars of Delphinus are located within the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).

[1] Covering 188.5 square degrees, corresponding to 0.457% of the sky, it ranks 69th of the 88 constellations in size.

[9] The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 14 segments.

The main asterism in Delphinus is Job's Coffin, nearly a 45°-apex lozenge or diamond of the four brightest stars: Alpha, Beta, Gamma, and Delta Delphini.

[3] Alpha Delphini is a blue-white hued main sequence star of magnitude 3.8,[10] 241 light-years from Earth.

[15] The gap between its close binary stars is visible from large amateur telescopes.

Struve 2725, called the "Ghost Double", is a pair that appears similar but dimmer.

[23][24] Zeta Delphini, an A3Va[25] main-sequence star of magnitude 4.6, was in 2014 discovered to have a brown dwarf orbiting around it.

[29] It took an unusually long time for the nova to reach peak brightness which indicate that it barely satisfied the conditions for a thermonuclear runaway.

[36] Arion was part of the first NameExoWorlds contest where the public got the opportunity to suggest names for exoplanets and their host stars.

[39] It was discovered from a single transit[40] in TESS data and it was confirmed by a network of citizen scientists.

The Neptunian-size planet was discovered from an abnormality from data retrieved from TOI-6883 c.[42] Its rich Milky Way star field means many modestly deep-sky objects.

[44] It is in the Shapley-Sawyer Concentration Class VIII[45] and is thought to share a common origin with another globular cluster in Boötes.

[48] At a distance of about 137,000 light-years,[46] the globular cluster NGC 7006 is at the outer reaches of the galaxy.