Radar imaging, as understood here, involves target recognition, i.e. the determination of the detailed properties of an object (size, shape, structure and composition, and also location and speed) from radar echoes returned by it. Advanced approaches are required for this, and several of recent interest are discussed in this book. They include mathematical inverse-scattering techniques based on the solution of integral equations; use of the singularity expansion method (SEM), related to the resonance scattering theory (RST), in which the pattern of resonance-frequency location in the complex frequency plane can be employed to characterize a given radar target; and the use of polarization information. Finally, the measurement of radar cross-sections is described.