Abstract While the of diffusion of technology has been extensively studied, a sysetematic treatment of origin of innovations is generally lacking. This has important implications for studies not only of the phenomenon of diffusion itself, but also for studies of long-term growth of productivity. This paper presents an investigation of technological; innovations in the farm tractor during a time period of nearly five decades from its genesis. It is concluded that the observed advances in technology are attributable to variations in farm size and experience acquired in the production and utilization of the tractor over the course of time. More generally, two main hypotheses of technological change emerge from the results of thus study. One is the hypothesis of learning i.e. that technological innovation originates in the accumulated experience of a practical nature. The other is the hypothesis of scaling, i.e. that the process of innovation is further governed by changes in the size of the larger system, within which the technology is embedded. However, certain widely believed alternative hypotheses of technological change do not seem to generally hold. It is concluded that technological development is an evolutionary process which is best understood in terms of an internal logic of its own.