The present article provides an overview about photovoltaic/thermal systems categorised by the temperature of the working fluid: Low-temperature (lower than 60º C), medium-temperature (between 60 and 90º C) and hightemperature (higher than 90º C). Concerning photovoltaic/thermal-air systems for low-temperature use, the majority of studies involve building-integrated non-concentrating systems with phase change materials and working-fluid temperatures at around 30-55º C. Concerning low-temperature photovoltaic/thermal-water systems, a large number of studies are about non-concentrating configurations appropriate for building-integrated and, in general, domestic applications with working fluids at approximately 50–60º C. Regarding nonconcentrating photovoltaic/thermal systems for medium-temperature use, a large number of references are appropriate for industrial and domestic applications (working fluids: air; water) with around 60-70º C workingfluid temperatures. The literature review about medium-temperature concentrating photovoltaic/thermal systems shows that the majority of investigations concern photovoltaic/thermal-water systems with concentration ratios up to 190X and working fluids at approximately 62-90º C, appropriate for domestic and waterdesalination applications. As for high-temperature concentrating photovoltaic/thermal systems, most of them have concentration ratios up to 1000X, involve parabolic concentrators and use water (as the working fluid) at around 100-250º C. Moreover, in the field of high-temperature photovoltaic/thermal systems, most of the configurations are appropriate for building and industrial applications, and consist of triple-junction or siliconbased photovoltaic/thermal cells. In light of the issues mentioned above, a critical discussion and key challenges (in terms of materials, efficiencies, technologies, etc.) are presented. The authors would like to thank ’’Ministerio de Economía y Competitividad’’ and “Ministerio de Ciencia e Innovación” of Spain for the funding (grant references ENE2016-81040-R and PID2019-111536RBI00). D. Chemisana thanks ’’Institució Catalana de Recerca i Estudis Avançats (ICREA)’’ for the ICREA Acadèmia award. Chr. Lamnatou is Lecturer of the Serra Húnter programme. Figures 1–6: reproduced with permission.