Optical imaging has always played a central role in the elucidation of biological and physiological mechanisms in modern biology and medicine. Based on the good experiences in light microscopy, sophisticated meso- and macroscopic optical imaging systems have recently been created. All optical imaging methods are characterized by high user-friendliness and sensitivity, they are associated with relatively low costs and do not require any radioactivity. Its clinical performance is seen in the intraoperative imaging of the tissue area to be removed and in the radiotracer-free diagnosis of diseases in body areas with good accessibility to light. From a pathomorphological point of view, the focus was particularly on the depiction of tumors and inflammation. Imaging detection of fluorescent dyes with emission characteristics in the near-infrared range of the spectrum is favorable in terms of a good signal-to-background ratio and improved information acquisition from greater tissue depths. A major challenge, however, is the diverse photon interactions with the tissue. Previous research and development work has produced various in vivo optical imaging methods, some of which are still in the experimental stage (e.g., fluorescence-mediated tomography, multispectral in vivo imaging, bioluminescence imaging, Raman spectroscopy), while others already have made their way into the clinical setting (e.g., fluorescence reflection imaging, optoacoustic imaging). The most important optical methods are presented in this review article.