Nanocrystalline　metals　have　many　functional　and　structural　applications　due　to　their　excellent　mechanical　properties　compared　to　their　coarse-grained　counterparts.　The　atomic-scale　understanding　of　the　deformation　mechanisms　of　nanocrystalline　metals　is　important　for　designing　new　materials,　novel　structures　and　applications.　The　review　presents　recent　developments　in　the　methods　and　techniques　for　in　situ　deformation　mechanism　investigations　on　face-centered-cubic　nanocrystalline　metals.　In　the　first　part,　we　will　briefly　introduce　some　important　techniques　that　have　been　used　for　investigating　the　deformation　behaviors　of　nanomaterials.　Then,　the　size　effects　and　the　plasticity　behaviors　in　nanocrystalline　metals　are　discussed　as　a　basis　for　comparison　with　the　plasticity　in　bulk　materials.　In　the　last　part,　we　show　the　atomic-scale　and　time-resolved　dynamic　deformation　processes　of　nanocrystalline　metals　using　our　in-lab　developed　deformation　device.　(C)　2018　Published　by　Elsevier　Ltd　on　behalf　of　The　editorial　office　of　Journal　of　Materials　Science　&　Technology.