The concept of nuclear waste forms based on minerals that contain actinides has led to the development of polyphase and special-purpose crystalline ceramics. These ceramics are considered by many to be attractive media for the long-term storage of actinides in geological repositories. The available data show that monazite, pyrochlore, zircon, and zirconolite are all highly durable in both natural and synthetic aqueous systems at low temperatures. In comparison, perovskite is prone to dissolution and conversion to anatase and other secondary alteration products. The titanate and silicate phases of interest become metamict (amorphous) as a result of irradiation. Several compounds, including monazite, cubic zirconia, and the defect fluorite structure types with Zr on the B site, exhibit the attractive property of radiation “resistance.” These results, together with other materials properties, are discussed briefly with respect to criteria for waste form performance.