In this article we construct a general duration model of technology adoption that incorporates the main factors discussed in different theories of diffusion of new process technologies. The model is applied to data on diffusion of CNC in the UK engineering industry. Although we find strong evidence in support of rank and endogenous learning effects, there seems to be little evidence in support of the stock and order effects. The main factors affecting the diffusion of CNC are found to be endogenous learning, firm size, industry growth rates, the cost of the technology, and expected changes in the cost of the technology.