Conventional migration tools have been implemented by the application of adjoint operators. Under simple circumstances this approach provides satisfactory results. In situations where the overburden is complex, scattering from the target is not simple, the acquisition geometry is irregular, or the waveforms are not spectrally balanced, adjoint operators often do not provide images of sufficient quality. These may be manifested as artifacts in the image, poor resolution, acquisition footprint or incomplete signature removal. In principle, we can use inversion to correct for these effects. Doing so can lead to images that are higher resolution, artifact-reduced, properly amplitude balanced and with a broadband spectrum (Wang et al., 2012).