The migration of full wavefields (primaries + multiples), using the concept of secondary sources at each subsurface gridpoint, is summarized. These secondary
sources are two-way and contain the gridpoint reflection as well as the gridpoint
transmission properties. They ’assist’ the primary sources in the illumination of the subsurface. Full wavefield migration is implemented as a closed-loop process where the estimated reflectivity properties are used to generate all higher-order scattering (multiples and transmission effects) such that the modeled full wavefield response matches the observed measurements. In addition, velocities can be updated simultaneously. Theoretical considerations and examples lead to the principal conclusion that multiples should be utilized, not removed.