Abstract: Comprised of essays arranged alphabetically from Absorbent Materials to X-Rays in Diagnostic Medicine, most on individual objects, artifacts, techniques, and products, this is an up-to-date reference work for all those involved in teaching or researching the history of twentieth-century technology, as well as the serious general reader. The core of each of the main entries is a technical description, within a historical narrative, of about 1,000 words plus illustrations and further reading. There are also about 30 longer survey entries that that address broad questions of technological systems, such as the context in which the various technologies were developed, discussions of any controversies and schools of thought, comparisons between different political and economics systems, and the various ways in which different nations have attempted to make and apply science and technology policies.