We are investigating solid-state dewetting of thin films as a technique for producing ordered arrays of metal nanoparticles over large areas. Such arrays are used as catalysts for nanowire and nanotube growth and may also be of interest in memory or plasmon device applications. When we begin with a single crystalline film, the dewetted nanoislands align along specific crystallographic orientations and show regular patterns. We observe a strong dependence of the morphological evolution of single crystalline nickel thin films on the thickness of the film and on the crystallographic orientation of the film, which is determined by an epitaxial relationship with a magnesium oxide substrate. The resulting nanoparticles remain epitaxial and thus share both in- and out-of -plane crystallographic alignment. In order to obtain similarly ordered dewetting with polycrystalline films, we employ physical templates. One technique is to physically constrain the area of film that dewets by pre-patterning a polycrystalline gold film on silicon dioxide. We observe that certain geometries lead to self-alignment of the dewetted nanoparticles (see Figure 1). Ongoing investigations will further characterize how film thickness and pattern dimensions affect the self-alignment.