Solar energy represents the best alternative for traditional energy sources used in many thermal energy systems. Among solar thermal systems, Flat Plate Solar Collectors (FPSCs) are the most utilized type implemented in low and medium-level thermal domestic applications. Recently, the usage of nanofluids (NFs) to enhance FPSCs is one of the newest technologies that has drawn the attention of researchers to improve the overall thermal efficiency of solar systems. This paper briefly reviews the recent studies carried on thermal performance enhancement of FPSCs by implementing NFs (single and hybrid NFs) considering the main influential parameters such as particle concentration, particle size, and collector area. Finally, the main obstacles reported by the researchers such as the instability, viscosity, concentration limit, corrosion effect and others are identified, which is believed to be useful for interested newcomers in this research area. Based on the studies investigated in this paper, NFs, even under low concentrations, can remarkably improve the energetic and exergetic efficiency of FPSCs.