I will overview seismic inversion methods for reconstructing the distribution of rock properties in the earth. Methods include traveltime tomography, reflection migration, and waveform tomography. They can be described as iterative backprojection of data residuals into the earth model. The backprojection is accomplished by applying the adjoint of the forward modeling operator to the data residuals. Appli- cations include exploration for oil and gas, mineral detec- tion, imaging the shallow subsurface for environmental assessment, and understanding tectonic processes by imaging the crust, mantle and core.