The supergalactic coordinate system is a convenient reference system used to locate distant galaxies, galaxy clusters and superclusters.

The supergalactic coordinate system was developed by Gérard de Vaucouleurs. The coordinate system has its equator aligned with the supergalactic plane, a major structure in the local universe formed by the preferential planar-like distribution of nearby galaxy clusters.

The supergalactic plane is roughly perpendicular the galactic plane of the Milky Way. Supergalactic longitude (SGL) is defined as 0⁰ where this supergalactic plane intersects the galactic plane. Because the supergalactic coordinate system is based on the supergalactic plane as observed from the Earth, it passes through the Earth. Objects on this supergalactic plane have a supergalactic latitude (SGB) of 0⁰.

The north supergalactic pole NSP (with SGB=90⁰) lies at Galactic coordinates l = 47.37⁰, b =+6.32⁰. The zero point (SGB=0⁰, SGL=0⁰) lies at l=137.37⁰, b=0⁰.

Supergalactic cartesian coordinates (SGX, SGY, SGZ) are also frequently used. In this system the supergalactic z-axis points towards the NSP, the supergalactic x-axis points towards the origin and the supergalactic y-axis is perpendicular to the both.