Due to their enhanced thermophysical properties, nanofluids have great potential for improving heat-transfer efficiency. Nanofluids are employed in various thermal applications in the automotive industry, heat exchangers, solar power generation and more. Among the applications of this technology, its use to enhance the heat transfer of solar collectors appears promising. It is therefore not a surprise that the use of nanofluids in solar collectors has become a popular research area. Still, there are important obstacles with the use of nanofluids in solar collectors. Stability is the most evident, in addition to environmental aspects and the need to design suitable large-scale production processes for the application of nanofluids at the required scale for large solar collectors’ fields. In this literature review, we study nanofluids in solar collectors, and parabolic-trough collectors in particular, at temperatures between 100 °C and 300 °C. We present recent advances and research on nanofluids and consider the progress in understanding stability mechanisms, characterization and preparation methods, as well as their thermophysical properties. We describe the main research gaps and suggest areas of further research.