The silence that greeted Adam McHugh's request for definitions of technology was in sharp contrast to the flurry of replies that usually greet a request posted here and is possibly indicative of the lack of concern among many economists with the details of technology and technological change, resulting in a paucity of precise definitions. Most students of economics are taught little about the details of technology and hence of the details of how technological change impacts on the economy. Many growth theorists model technology as hidden in the black box of an aggregate neoclassical production function, whether they model technological change as exogenous, as did Solow, or endogenous, as did Romer. Nathan Rosenberg has broken open that black box in several publications, such as "Inside and Black Box" and "Exploring the Black Box". But his work has had little impact on most growth theorists who continue to model technology as "flat" whose nature is captured by the form of the aggregate production function and whose changes are modelled by shifts in a parameter "A" in production functions such as Y = Af(Labour, Physical Capital, Human Capital). Little attention is usually paid to defining technology in such cases but the implicit definition is "that which determines the form of the aggregate production function, and changes in which alter the parameter A, or the efficiency units in which in the inputs are measured". In our forthcoming book "Economic Transformations: General Purpose Technologies and Long Term Economic Growth" (Lipsey, Carlaw and Bekar, OUP November 2005), we consider various definitions of technology and then define it as follows (page 58-9) "Definition: Technological knowledge, technology for short, is the set of ideas specifying all activities that create economic value. It comprises: (1) knowledge about product technologies, the specifications of everything that is produced; (2) knowledge about process technologies, the specifications of all processes by which goods and services are produced; (3) knowledge about organisational technologies, the specification of how productive activity is organized in productive and administrative units for producing present and future goods and services (which thus includes knowledge about how to conduct R&D)." "This definition distinguishes technological knowledge from other types of knowledge, including scientific knowledge. As with all definitions, there are grey areas at the boundaries. In particular, some things are excluded that come close to being what we might think of as technological knowledge. For example, knowledge about some physical process is scientific knowledge until it is put to use to make something of economic value. When that is done, the knowledge that does the job becomes technological knowledge. So, for example, Newton's laws of motion are scientific knowledge but when they were used to make a better water wheel, the knowledge of how to do so is technological. We might say that it embodies or uses the scientific knowledge that is Newton's laws, but the specification of how to make the wheel is technological." "Although all capital goods embody technological knowledge, they are not themselves technology. Although it is humans who know how to construct and operate the things that create economic value, the embodiment of this knowledge in their memory circuits is not technology. Although technology is embodied in both physical and human capital, it is distinct from both." This broad definition is intended to define technology in a way that is suitable to studying the details of technological change as the prime engine of long term economic growth and modelling it in a structured (non-flat) manner. Richard G. Lipsey