Particles on a planar surface usually pack into a simple triangular lattice. How does this change if curvature is switched on? The minimum energy configuration for repulsively interacting particles on curved surfaces is a challenging problem with applications to a variety of biological, chemical and condensed matter systems. I will discuss the universal proliferation of novel defect arrays (``scars'') in the ground state of crystals of a variety of topologies, including experimental results for self-assembled spherical colloidal crystals and paraboloidal bubble rafts. Defect arrays may aid in the design of meso-atoms for supra-moldecular assembly. Finally I will discuss the kinetics of scar formation and the instability of interstitials in curved space.