Photoacoustic imaging, frequently coregistered with ultrasonic imaging, can provide functional and cellular/molecular information about tissue within the anatomical landmarks of an imaged region. This review details the fundamentals of photoacoustic imaging and its most promising imaging applications. Particular attention is paid to photoacoustic imaging's relationship with ultrasound, focusing on distinct differences and similarities between the two modalities and highlighting the mutual benefit of using both concurrently in certain preclinical and clinical applications. Much like its origins as an imaging modality were intertwined with ultrasonic imaging (namely, its acoustic transducers and hardware), the future of photoacoustic imaging-particularly in the clinical arena-similarly depends on ultrasound and its time-tested ability to provide real-time visualization of soft tissue.