This paper explores the main determinants of productivity growth. The analysis is performed using Spanish firm-level data. We define a framework where the relative magnitudes of alternative, but not exclusive, sources of technical change are simultaneously estimated. Our main finding is that the average total factor productivity (TFP) growth is fully explained by embodied technical progress (i.e., either new capital goods or human capital). Our results contradict the existence of a positive contribution of economywide neutral technological progress in determining average TFP growth. They also leave little room for large, unpriced effects external to the firm, both at the aggregate and at the industry level. We find evidence of firm-specific learning by doing, short-lived and due to adoption of new processes.