Technological innovation, of product or process types, is discussed in terms of "demand pull" and "technology push" motivations. Five models of product quality change are developed. Two models view the problem as one of finding the appropriate scalar proxy, assuming users value the product equivalently, and changes in preferences, or uniform changes due to technology push are the principal driving force. In the third model technological capability is expressed by a vector rather than a scalar; it is then possible to investigate the number of trade-off relationships among performance dimensions, and interpretation of what they capture should relate to demand pull and technology push motivations. Model four is formulated in terms of the average rates of change in product attributes over the length of the product's development program. The fifth model attempts to identify mutually exclusive market categories. In the appendix three models are employed for an empirical analysis of product quality change in the computer and machine tool industries.