Single-site　heterogeneous　catalysts　constructed　with　highly　dispersed,　spatially　well-separated　isolated　species　have　attracted　much　attention　due　to　their　outstanding　specific　activity　and　selectivity　attributable　to　the　unsaturated　surface　coordination　sites　and　unique　local　electronic　structures.　Furthermore,　such　single-site　heterogeneous　catalysts　are　considered　to　be　attractive　as　models　for　the　top　surface　of　inorganic　semiconducting　materials.　As　catalysts　and　photocatalysts,　they　provide　suitable　reaction　fields　to　investigate　the　relationship　between　the　activity　and　local　structure　of　the　active　sites.　To　obtain　detailed　information　on　the　reaction　mechanism　at　the　molecular　level,　advanced　characterization　techniques　such　as　X-ray　absorption　fine-structure　spectroscopy　(XAFS),　FT-IR,　UV–VIS,　EPR,　and　photoluminescence　spectroscopy　were　applied.　Moreover,　various　solid　materials　such　as　silica,　mesoporous　materials　including　zeolites,　and　semiconducting　materials　offer　applicable　strategies　to　design　unique　single-site　heterogeneous　photocatalysts.　In　the　present　review,　photocatalytic　reactions　on　single-site　heterogeneous　catalysts　constructed　on　semiconducting　materials　have　been　summarized.　Special　attention　has　been　focused　on　photocatalytic　reactions　for　clean　energy　such　as　the　splitting　of　water,　reduction　of　carbon　dioxide　with　H2O,　conversion　of　CH4,　and　fixation　of　nitrogen.　Furthermore,　the　preparation　of　single-site　heterogeneous　catalysts,　their　characterizations,　and　the　relationship　between　their　local　structures　and　photocatalytic　activities　are　also　discussed.　The　present　review　not　only　provides　a　systematic　understanding　of　single-site　heterogeneous　photocatalysts　but　also　an　understanding　of　the　reaction　mechanisms　of　semiconducting　photocatalysis　at　the　atomic　level　as　well　as　the　design　of　high-performance　catalytic　and　photocatalytic　reaction　systems.　Graphical　Abstract:　[Figure　not　available:　see　fulltext.].　©　2022,　The　Author(s),　under　exclusive　licence　to　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature.