Optogenetic light sensing systems exploit photosensory modules to control protein-protein interaction and protein function with light. Optogenetic approaches involve the engineering of a chimeric construct with the introduction of light sensing motifs. The function of the chimeric product can be manipulated through the light-induced conformational change, which either alters the spatial position of a target protein or introduces an intrinsic disorder in the target protein. This technique creates an internal light switch that allows the activity of the target molecule to be modulated in a living cell. It has been demonstrated to control small GTPase activity, transcription factor, and protein-protein interaction. This Methods Collection includes recent advances of applying engineered optogenetic tools in biomedicine, stem cell therapy, drug development, and drug delivery. Applications of optogenetic tools are expected to bring innovative solutions for minimally invasive therapy, cell therapy, and controlled drug delivery.