Surface plasmons provide a pathway to efficiently absorb and confine light in metallic nanostructures, thereby bridging photonics to the nano scale. The decay of surface plasmons generates energetic ‘hot’ carriers, which can drive chemical reactions or be injected into semiconductors for nano-scale photochemical or photovoltaic energy conversion. Novel plasmonic hot carrier devices and architectures continue to be demonstrated, but the complexity of the underlying processes make a complete microscopic understanding of all the mechanisms and design considerations for such devices extremely challenging. Here,we review the theoretical and computational efforts to understand and model plasmonic hot carrier devices. We split the problem into three steps: hot carrier generation, transport and collection, and review theoretical approaches with the appropriate level of detail for each step along with their predictions. We identify the key advances necessary to complete the microscopic mechanistic picture and facilitate the design of the next generation of devices and materials for plasmonic energy conversion.