This chapter discusses saturation of defects produced in metals at high densities. During continuous irradiation at low temperatures, the immobile atomic defects will accumulate in the lattice and some of the newly formed defects will recombine or cluster with already existing ones. As a consequence, the defect structure will change and the damage rate will decrease. The damage rate will become zero at a saturation resistivity Δρs. This chapter presents data of maximum experimental resistivity changes Δρmax, saturation resistivities Δρs and recombination volumes v0. All v0 data have been reevaluated with “best” ρF values. A comparison of data from different particles shows an increase of v0 with increasing hardness of the recoil spectrum. The recombination volume decreases approximately reciprocally with increasing irradiation temperature.