A terminal guidance and/or steering process for a projectile towards a target, process in which the orientation of a velocity vector {right arrow over (Vp)} is determined then a guidance law is applied and finally a steering algorithm enabling the projectile to be reoriented towards its target, process wherein the three components of the terrestrial magnetic field {right arrow over (H)} are measured in a projectile-linked reference marker (Ox.sub.mY.sub.mZ.sub.m) and these measurements are used in the guidance law and/or steering algorithm as a fixed reference marker enabling the orientation at least partially of the projectile-linked reference marker with respect to the terrestrial reference marker (GX.sub.fY.sub.fZ.sub.f).