Sub-micron　and　nanostructured　materials　exhibit　high　strength,　ultra-large　elasticity　and　unusual　plastic　deformation　behaviors.　These　properties　are　important　for　their　applications　as　building　blocks　for　the　fabrication　of　nano-and　micro-devices　as　well　as　for　their　use　as　components　for　composite　materials,　high-strength　structural　and　novel　functional　materials.　These　nano-related　deformation　and　mechanical　behaviors,　which　are　derived　from　possible　size　and　dimensional　effects　and　the　low　density　of　defects,　are　considerably　different　from　their　conventional　bulk　counterparts.　The　atomic-scale　understanding　of　the　microstructural　evolution　process　of　nanomaterials　when　they　are　subjected　to　external　stress　is　crucial　for　understanding　these　＇unusual＇　phenomena　and　is　important　for　designing　new　materials,　novel　structures　and　applications.　This　review　presents　the　recent　developments　in　the　methods,　techniques,　instrumentation　and　scientific　progress　for　atomic-scale　in　situ　deformation　dynamics　on　nanomaterials,　including　nanowires,　nanotubes,　nanocrystals,　nanofilms　and　polycrystalline　nanomaterials.　The　unusual　dislocation　initiation,　partial-full　dislocation　transition,　crystalline-amorphous　transitions　and　fracture　phenomena　related　to　the　experimental　mechanics　of　the　nanomaterials　are　reviewed.　Current　limitations　and　future　aspects　using　in　situ　high-resolution　transmission　electron　microscopy　of　nanomaterials　are　also　discussed.　A　new　research　field　of　in　situ　experimental　mechanics　at　the　atomic　scale　is　thus　expected.　NPG　Asia　Materials　(2013)　5,　e40;　doi:10.1038/am.2012.70;　published　online　15　February　2013