© 2021, Akadémiai Kiadó, Budapest, Hungary.Enhancement in properties of thermal storage materials improves their performance and contributes to reducing the greenhouse gas emissions. The enhancement can be made in a passive way, which is cost-effective and hardly requires management. For decades, phase change materials (PCMs) have been used in many applications for thermal storage, thermal control and thermal insulation purposes. PCM can store a huge amount of energy with low or no temperature swing. However, the major drawback of PCM is the low thermal conductivity. Techniques of different scales (macroscopic, microscopic and nanoscopic) have been adopted in thermal engineering to enhance the thermal conductivity of PCM. This paper presents a comprehensive review of the literature dealing with micro/nano enhancement techniques of PCMs. Enhancement effects as well as limitations of each technique are discussed in detail. Moreover, direction for future research and possible challenges are pointed out along with conclusions drawn from the studies.