The thermal, fluid flow, and tritium release problems represent a major part of the research and development issues for liquid-metal and solid breeder blankets. The issues are characterized, and recent progress in model development and experiments is described. The issues for liquid-metal blankets are dominated by magnetohydrodynamic (MHD) effects on fluid flow and heat transfer. New design solutions have been proposed, new facilities have been constructed, and models are being developed to address MHD effects. The problems of solid breeder blankets are dominated by tritium release, containment, and inventory. There has been remarkable progress in understanding tritium transport in solid breeders because of successful irradiation experiments of solid breeders in fusion reactors. New models on tritium transport have provided key tools for the analysis and interpretation of the experimental results, A new issue related to thermal control in solid breeder is the subject of active experimental and modeling effort.