Ammonia　(NH3)　is　closely　related　to　the　fields　of　food　and　energy　that　humans　depend　on.　The　exploitation　of　advanced　catalysts　for　NH3　synthesis　has　been　a　research　hotspot　for　more　than　one　hundred　years.　Previous　studies　have　shown　that　the　Ru　B5　sites　(step　sites　on　the　Ru　(0001)　surface　uniquely　arranged　with　five　Ru　atoms)　and　Fe　C7　sites　(iron　atoms　with　seven　nearest　neighbors)　over　nanoparticle　catalysts　are　highly　reactive　for　N2-to-NH3　conversion.　In　recent　years,　single-atom　and　cluster　catalysts,　where　the　B5　sites　and　C7　sites　are　absent,　have　emerged　as　promising　catalysts　for　efficient　NH3　synthesis.　In　this　review,　we　focus　on　the　recent　advances　in　single-atom　and　cluster　catalysts,　including　single-atom　catalysts　(SACs),　single-cluster　catalysts　(SCCs),　and　bimetallic-cluster　catalysts　(BCCs),　for　thermocatalytic　NH3　synthesis　at　mild　conditions.　In　addition,　we　discussed　and　summarized　the　unique　structural　properties　and　reaction　performance　as　well　as　reaction　mechanisms　over　single-atom　and　cluster　catalysts　in　comparison　with　traditional　nanoparticle　catalysts.　Finally,　the　challenges　and　prospects　in　the　rational　design　of　efficient　single-atom　and　cluster　catalysts　for　NH3　synthesis　were　provided.　Recent　advances　in　single-atom　and　cluster　catalysts,　including　single-atom　catalysts　(SACs),　single-cluster　catalysts　(SCCs),　and　bimetallic-cluster　catalysts　(BCCs),　for　thermocatalytic　NH3　synthesis　at　mild　conditions.