Over the past decades, photothermal agents have been studied extensively for photothermal therapy, photoacoustic imaging, and drug delivery. Photothermal reagents with excellent performance can enable safe, low-damage, and targeted photothermal therapy. In addition, some photothermal reagents, such as Au and MnO2 nanoparticles, can be used as drug carriers for drug delivery and achieve controlled drug release through their photothermal properties. Previous research has demonstrated promising results in in vitro and small animal models. This proposed Methods Collection focuses on the development of photothermal reagents and their applications in photothermal therapy, imaging, and drug delivery. In addition to the basic tumors model, the model includes several other disease models that can be treated with photothermal therapy. The following are the objectives of this Methods Collection: 1) Development of photothermal agents for photothermal therapy, imaging, and drug delivery 2) Investigate the molecular mechanism of photothermal therapy using in vitro or in vivo models