Single-atom　catalysts　(SACs)　have　emerged　as　a　focal　point　of　research　in　the　field　of　heterogeneous　catalysis.　This　paper　reviews　the　progress　in　the　studies　of　single　atoms　as　promoters　in　various　catalytic　reactions,　elucidating　their　distinctive　role　in　comparison　to　the　dominant　active　sites.　We　provide　a　discussion　on　the　application　of　single-atom　promoters　(SAP)　within　host-guest　systems　in　various　catalysts,　including　metal　oxide　supported　catalysts,　molybdenum　carbide-based　catalysts,　bimetallic　catalysts,　and　others.　The　behavior　of　SAP　is　diverse.　They　often　promote　the　formation　of　oxygen　vacancies　for　oxide　support,　leading　to　local　site　reconstruction　that　creates　specific　reaction　route.　Moreover,　they　can　also　precisely　modify　the　electronic　structure　of　hetero-metal　atomic　or　nanoparticle　sites,　then　regulating　the　adsorption　of　reactants　or　intermediates　and　catalytic　performance.　Finally,　the　potential　for　the　development　of　SAP　is　outlined,　proposing　novel　approach　for　the　design　of　SACs　with　enhanced　activity　and　stability.　©　2025　Wiley-VCH　GmbH.