Note: Modules marked with (**) are new Modules added in SMIL2.1. Modules marked with (*) are revised modules from SMIL 2.0
| Module Name | specified in |
| AccessKeyTiming | SMIL 21 Timing |
| AlignmentLayout (**) | SMIL 21 Layout |
| AudioLayout | SMIL 21 Layout |
| BackgroundTilingLayout (**) | SMIL 21 Layout |
| BasicAnimation | SMIL 21 Animation |
| BasicContentControl | SMIL 21 ContentControl |
| BasicInlineTiming | SMIL 21 Timing |
| BasicExclTimeContainers (**) | SMIL 21 Timing |
| BasicLayout (*) | SMIL 21 Layout |
| BasicLinking | SMIL 21 Linking |
| BasicMedia | SMIL 21 Media Object |
| BasicPriorityClassContainers (**) | SMIL 21 Timing |
| BasicTimeContainers | SMIL 21 Timing |
| BasicTransitions (*) | SMIL 21 Transitions |
| BrushMedia | SMIL 21 Media Object |
| CustomTestAttributes | SMIL 21 ContentControl |
| EventTiming | SMIL 21 Timing |
| ExclTimeContainers | former SMIL20 module REMOVED in SMIL2.1 |
| FillDefault | SMIL 21 Timing |
| FullScreenTransitionEffects (**) | SMIL 21 Transitions |
| HierarchicalLayout | former SMIL20 module REMOVED in SMIL2.1 |
| InlineTransitions | SMIL 21 Transitions |
| LinkingAttributes | SMIL 21 Linking |
| MediaAccessibility | SMIL 21 Media Object |
| MediaClipMarkers | SMIL 21 Media Object |
| MediaClipping | SMIL 21 Media Object |
| MediaDescription | SMIL 21 Media Object |
| MediaMarkerTiming | SMIL 21 Timing |
| MediaParam (*) | SMIL 21 Media Object |
| Metainformation | SMIL 21 Metadata |
| MinMaxTiming | SMIL 21 Timing |
| MultiArcTiming | SMIL 21 Timing |
| MultiWindowLayout (*) | SMIL 21 Layout |
| ObjectLinking | SMIL 21 Linking |
| OverrideLayout (**) | SMIL 21 Layout |
| PrefetchControl | SMIL 21 ContentControl |
| RepeatTiming | SMIL 21 Timing |
| RepeatValueTiming | SMIL 21 Timing |
| RestartDefault | SMIL 21 Timing |
| RestartTiming | SMIL 21 Timing |
| SkipContentControl | SMIL 21 ContentControl |
| SplineAnimation | SMIL 21 Animation |
| Structure | SMIL 21 Structure |
| SubRegionLayout (**) | SMIL 21 Layout |
| SyncbaseTiming | SMIL 21 Timing |
| SyncBehavior | SMIL 21 Timing |
| SyncBehaviorDefault | SMIL 21 Timing |
| SyncMaster | SMIL 21 Timing |
| TimeContainerAttributes | SMIL 21 Timing |
| TimeManipulations | SMIL 21 Time manipulations |
| TransitionModifiers | SMIL 21 Transitions |
| WallclockTiming | SMIL 21 Timing |