This article presents a review on Li diffusion in lithium containing metal oxide compounds. The focus is on the investigation of solid state diffusion by tracer methods. In contrast to experiments with Nuclear Magnetic Resonance Spectroscopy and Impedance Spectroscopy, only a limited number of tracer based experiments can be found in the literature. Possible reasons are discussed. Measurements on the system Li-Nb-O are given in detail, while additional results on other Li-M-O (M = Al, Si, Mn, Ti) systems are also presented. The review is completed by a brief survey of the experimental methods in use.