Due　to　the　expensive　price　and　the　low　reserve　of　noble　metals　in　nature,　much　attention　has　been　paid　to　single-atom　catalysts　(SACs)-especially　single-atom　noble　metal　catalysts-owing　to　their　maximum　atomic　utilization　and　dispersion.　The　emergence　of　SACs　greatly　decreases　the　amount　of　precious　metals,　improves　the　catalytic　activity,　and　makes　the　catalytic　process　progressively　economic　and　sustainable.　However,　the　most　remarkable　challenge　is　the　active　sites　and　their　stability　against　migration　and　aggregation　under　practical　conditions.　This　review　article　summarizes　the　preparation　strategies　of　SACs　and　their　catalytic　applications　for　the　oxidation　of　methane,　carbon　monoxide,　and　volatile　organic　compounds　(VOCs)　and　the　reduction　of　nitrogen　oxides.　Furthermore,　the　perspectives　and　challenges　of　SACs　in　future　research　and　practical　applications　are　proposed.　It　is　envisioned　that　the　results　summarized　in　this　review　will　stimulate　the　interest　of　more　researchers　in　developing　SACs　that　are　effective　in　catalyzing　the　reactions　related　to　the　environmental　pollution　control.