Thermophysical and thermochemical data on ceramic lithium compounds proposed as tritium breeding material for the solid breeder concept of fusion reactors using a purge gas to continuously extract the tritium bred are discussed. Diffusion coefficients for tritium in these materials from the data of tritium extraction experiments reported in the literature are critically examined and reevaluated. The effect of the diffusion rate and of the solubility of tritium on the tritium inventory in the breeder material is discussed. Only extended “in-pile” experiments in fission reactors can answer the question whether or not the application of a solid breeder concept is really feasible in a future fusion reactor.