Delphinus (Latin, "dolphin") is a constellation in the northern sky, close to the celestial equator. It is one of the smaller constellations, ranked 69th in size out of 88. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical Union.

Delphinus's brightest stars form a distinctive asterism that can easily be recognized. It is bordered (clockwise from north) by Vulpecula the fox, Sagitta the arrow, Aquila the eagle, Aquarius the water-carrier, Equuleus the foal and Pegasus the flying horse.

The two brightest stars of this constellation, Sualocin (Alpha Delphini) and Rotanev (Beta Delphini), are not names dating from antiquity, but instead date from a star catalogue of 1814 that was published at the Palermo Observatory in Italy. When read backwards, they form the name Nicolaus Venator which is the Latinized version of the name of the assistant director of that observatory at that time, Niccolò Cacciatore (both Cacciatore and Venator mean hunter).

In Greek mythology, the god Poseidon wanted to marry Amphitrite, a beautiful nereid. She, however, wanting to protect her virginity, fled to the Atlas mountains. Her suitor then sent out several searchers, among them a certain Delphinus. Delphinus accidentally stumbled upon her and was able to persuade Amphitrite to accept Poseidon's wooing. Out of gratitude the god placed the image of a dolphin among the stars.