Nanoscale plasticity has been studied on (0001) GaN thin films, using tips with very small radius of curvature. Cross-section transmission electron microscopy images of the nanoindentations indicate that the primary slip systems are the pyramidal {11¯01}⟨112¯3⟩ and {112¯2}⟨112¯3⟩, followed by the basal {0002}⟨112¯0⟩. Incipient plasticity was observed to be initiated by metastable atomic-scale slip events that occur as the crystal conforms to the shape of the tip. Large volumetric material displacements along the {11¯01}⟨112¯3⟩ and {112¯2}⟨112¯3⟩ slip systems were observed at an average shear stress of 11 GPa. Hexagonal shaped nanoindentation impressions following the symmetry of GaN were observed, with material pile-up in the ⟨112¯0⟩ directions. Spatially resolved cathodoluminescence images were used to correlate the microstructure with the optical properties. A large number of non-radiative defects were observed directly below the indentation. Regions under tensile stress extending from the nanoindentation along ⟨112¯0⟩ directions were associated with the {0002}⟨112¯0⟩ slip.