 Recent advances in plasmonic nanoparticles have led to exciting developments in energy, catalyst chemistry, optics, biotechnology, and medicine, with photothermal properties being of enormous interest in biomedical fields due to their strong optical response and ability to manipulate the photothermal effect by external light sources. While most biomedical applications have focused on photothermal therapy, further exploration of photothermal effect-based diagnosis, treatment, and theranostics is needed to fully realize the potential of these particles for clinical and other applications with future directions including better understanding and control of fundamental properties and expansion into new areas such as sensing and imaging. This article was authored by Miho Kim, Yonghoon Lee, and Zhuomin Nam.