This　paper　reports　an　in-situ　study　of　the　plastic　deformation　behavior　of　surface　grains　in　a　polycrystalline　aluminum　alloy,　in　particular　the　active　slip　systems　and　lattice　rotation,　by　means　of　the　electron　backscattered　diffraction　method.　The　experimental　analysis　is　conducted　at　a　spatial　resolution　of　1　mu　m,　thus　allowing　detailed　analysis　at　subgrain　levels,　enabling　elucidation　of　fine　details　of　the　deformation　process　that　are　not　commonly　seen　in　the　literature.　It　is　found　that　the　grains　rotate　gradually　with　increasing　strain　during　tensile　deformation.　The　lattice　rotation,　in　terms　of　both　rotation　path　and　rotation　rate,　is　highly　inhomogeneous　both　among　the　grains　and　within　individual　grains,　leading　to　the　formation　of　subgrains.　The　rotation　behavior　can　be　adequately　described　by　the　activation　of　slip　systems　with　the　maximum　and　second　maximum　Schmid　factors.　The　number　of　independent　slip　systems　in　surface　grains　is　much　fewer　than　that　in　interior　grains,　as　predicted　by　crystal　plasticity　theories.　The　lattice　rotation　rate　is　also　heterogeneous　among　grains　and　subregions　and　for　different　deformation　stages.　The　differences　in　rotation　rate　provide　another　mechanism　for　the　accommodation　of　plastic　strains　and　for　the　creation　of　subgrains.　These　findings　are　of　importance　for　the　mechanical　processing　of　thin　sheet　materials　or　the　deformation　behavior　of　miniature　components,　where　the　majority　of　grains　are　on　the　surfaces.　(C)　2013　Elsevier　B.V.　All　rights　reserved.