Trilateration is the use of distances (or "ranges") for determining the unknown position coordinates of a point of interest, often around Earth (geopositioning). When more than three distances are involved, it may be called multilateration, for emphasis.

The distances or ranges might be ordinary Euclidean distances (slant ranges) or spherical distances (scaled central angles), as in true-range multilateration; or biased distances (pseudo-ranges), as in pseudo-range multilateration.

Trilateration or multilateration should not be confused with triangulation, which uses angles for positioning; and direction finding, which determines the line of sight direction to a target without determining the radial distance.