Actinide solids 5f dependence of physical properties.- The preparation of high purity actinide metals and compounds.- Structural and thermodynamic properties of actinide solids and their relation to bonding.- Magnetic properties of actinide solids.- Localization and hybridization of 5f states in the metallic and ionic bond as investigated by photoelectron spectroscopy.- The theory of 5f bonding in actinide solids.- General conclusions and trends in actinide research.