Nanofluids are a new generation of heat transfer fluids that have attracted researchers' attention from diverse fields due to their anomalous thermal behavior and potential applications. In the past few decades, numerous studies have been carried out to investigate the thermal properties of nanofluids. A long-term stability is the first basic requirement in nanofluids research for maintaining their enhanced thermophysical properties. Thus, a holistic approach including stability and thermophysical properties is needed to achieve the synthesis of nanofluids with outstanding thermal properties. In this paper, a comprehensive literature on the synthesis, stability, thermophysical properties, and the characterization of nanofluids has been reviewed. Moreover, the factors that influence the thermophysical properties have been discussed. Finally, the applications and challenges of nanofluids have been mentioned. This paper provides an extensive review on nanofluids that critically summarizes and analyzes the recent research studies on nanofluids and sheds light on gaps, opportunities and further enhancement towards performance improvement of nanofluids. (C) 2018 Elsevier B.V. All rights reserved.