Photoacoustic imaging (PAI) is a functional optical imaging modality that utilizes ultrasound as a medium. Owing to its high contrast in optical imaging and deep tissue penetration capabilities inherent in ultrasound, PAI can generate images that integrate both structural and functional information. It has emerged as a novel medical imaging tool, with ongoing research continually expanding its applications within the medical field. The integration of photoacoustic imaging with other modalities to create multimodal imaging systems allows for the synergistic advantages of various technologies, thereby providing more comprehensive diagnostic information. PAI facilitates early and precise diagnosis as well as treatment monitoring for diverse conditions such as tumors, inflammation, and skeletal muscle injuries through real-time quantitative analysis of deoxyhemoglobin levels and molecular markers. This article elucidates the principles of PAI, its various modes of operation, and clinical applications while also anticipating future developmental prospects.