A review of thick-film sensors is presented. The evolution of the technology to a successful enabling mechanism for solid-state sensors is described. Many examples of applications in the major signal domains (mechanical, radiant, thermal, magnetic and chemical) are cited. The important characteristics of the technology relating to hybrid circuits, support structures and primary sensing elements are illustrated. The future of thick-film sensors is discussed in the light of the rapid development of new materials for sensors that have emerged over recent years.