This　book　introduces　the　reliability　modelling　and　optimization　of　warm　standby　systems.　Warm　standby　is　an　attractive　redundancy　technique,　as　it　consumes　less　energy　than　hot　standby　and　switches　into　the　active　state　faster　than　cold　standby.　Since　a　warm　standby　component　experiences　different　failure　rates　in　the　standby　state　and　active　state,　the　reliability　evaluation　is　challenging　and　the　existing　works　are　only　restricted　to　very　special　cases.　By　adapting　the　decision　diagrams,　this　book　proposes　the　methodology　to　evaluate　the　reliability　of　different　types　of　warm　standby　systems　and　studies　the　reliability　optimization.　Compared　with　existing　works,　the　proposed　methods　allow　the　system　to　have　an　arbitrary　number　of　components　and　allow　the　failure　time　distribution　of　components　to　observe　arbitrary　distributions.　From　this　book,　the　readers　can　not　only　learn　how　to　evaluate　and　optimize　the　reliability　of　warm　standby　systems　but　also　use　the　methods　to　study　the　reliability　of　other　complex　systems.　©　National　Defense　Industry　Press　2021.