The paper discusses the diffusion of new technologies from the perspective of the classical economists and Schumpeter. After a comparison of the pre- and post-technical change long-period positions of the economy, we illustrate the process of transition between the two in terms of a two-sector model. Next, we turn to a system with joint production. The fact that some products may be “bads” that need to be disposed of leads to a study of systems of production-cum-disposal. Finally, we investigate the selection pressure innovations exert on incumbent firms. An important message is that technical change cannot generally be studied within a partial framework of the analysis.