This chapter shows an example of how seismic wave theory can be used to improve cross-sectional images of subsurface zones with complex geological structure prepared from seismic data. In CMP stack sections, which are basic images of the subsurface constructed from seismograms, the reflectors and layer interfaces are generally not in their correct spatial positions. Seismic migration is a process that attempts to move them to their correct spatial positions. This chapter shows how seismic wave theory can be used to develop the methods of seismic wave equation migration. As an introduction, the chapter begins with basic methods for migrating point and dipping reflectors and describes the relatively simple methods for diffraction-summation and wavefront migration.This is followed by coverage of the basic wave equation migration methods, namely phase-shift migration, frequency-wavenumber migration, finite difference migration, and Kirchoff migration. A brief explanation of the need for depth migration, which is an improvement over the wave equation migration methods, is also provided.