Parabolic Trough Collectors (PTC) are one of the most widely used technology amongst the solar thermal systems used by the power generation industry. In recent years, numerous scientific investigations have focused on this topic to assess the thermal performance and to improve its thermal efficiency. The current paper presents a short but concise review of the PTC system showing the recent and past studies in a quest to improve and enhance the thermal and optical efficiencies. We discuss briefly the techniques used for single and two-phase flow modelling, design variables and experimental processes. Furthermore, studies investigating the enhancement of thermal performance are critically summarized such as: use of nanofluids as a working fluid and passive heat transfer enhancement techniques (inserts for the solar receiver).