This paper presents a model of firm-level productivity growth that distinguishes between innovation and technology diffusion, and then applies the model to a large-scale data set of Japanese manufacturing and non-manufacturing firms between 1994 and 2000. We find both innovation and diffusion are important factors in firm-level productivity growth. Results also suggest that innovation comes not only directly from R&D activities, but also indirectly from patent purchases and imports. Previously, patent purchases and imports were considered as sources of technology diffusion rather than innovation. In fact, we find patent purchases are more effective in this regard than R&D expenditure.