In this chapter, the concepts and fundamentals of PV/T collectors are provided in a simplistic manner along with mathematical models that help in evaluating the performance of these systems. The chapter emphasizes traditional PV/T collectors, namely air-based PV/T, water-based PV/T and the combination of air and water as working fluids for PV/T systems. Traditional PV/T collectors are essentially the simplest types that were proposed in the literature. Although the combinational type, which utilizes both air and water, is more complicated. Furthermore, the chapter investigates some of the traditional PV/T design configurations that have been adopted at research level. © 2024, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.