Recent studies on the exploitation of novel organic radical compounds that exhibit photo-responsive properties by illumination are described in this tutorial review. Those so far reported consist of a variety of photo-responsive pi-electron moieties such as azobenzene, diarylethene, biindenylidene, terphenoquinone, anthracene, naphthopyran, arylimine, or hexaarylbiimidazoles, bearing stable organic radicals or generating organic radicals as spin centres for magnetic properties. The switching behaviours of their magnetic properties evoked by the stimuli of irradiation are discussed by taking the associated structural changes into consideration.