Photothermal nanomaterials with a unique light-to-heat conversion property have great technological implications in a variety of areas ranging from biomedical to environmental applications. This book chapter summarizes the recent development of various light absorbing materials with photothermal effects into four functional categories, including plasmonic metals, semiconductors, carbon-, and polymer-based materials. The photothermal materials of these categories can be assembled and form hybrids or composites for enhanced photothermal performance. The different mechanisms of photothermal conversion as well as the potential applications in photothermal therapy, photothermal sterilization, and solar-driven water evaporation are discussed. Special attention is devoted to strategies that have been developed for improving the light absorption and light-to-heat conversion capabilities of these photothermal materials by tailoring the size, shape, composition, surface functionalities, bandgap, etc. Finally, the perspectives and challenges of the future development of photothermal materials are presented.