Variable　emissivity　material　(VEM)　can　dynamically　vary　its　emissivity　and　infrared　radiation　under　certain　conditions,　which　may　find　potential　applications　in　infrared　stealth/camouflage,　solar　thermal　collector,　spacecraft　thermal　control,　and　smart　energy-saving　windows.　In　this　paper,　the　variable　emissivity　materials　and　devices　based　on　electrochromism　and　thermochromism　are　introduced.　The　basic　principle　and　present　status　of　the　research　in　these　fields　are　overviewed.　Four　kinds　of　representative　VEMs　are　extensively　summarized,　which　are　tungsten　trioxides　(WO3),　conducting　polymers　(CPs),　perovskite　oxides　(A(1-x)B(x)MO(3)),　and　vanadium　dioxide　(VO2).　Finally,　specific　issues　confronted　with　electrochromic　and　thermochromic　materials　and　devices　are　prospected.