Ga-based liquid metal has obtained great attention because of its excellent physical and chemical properties, such as extraordinary thermal conductivity, high electrical conductivity, excellent fluidity. Thus, liquid metal has increasingly been used in many applications, including the microfluidics, biomedical applications, flexible electronics, soft machines and thermal management. Signiﬁcant progress in science and industry has been made in the past two decades about theGa-based liquid metal. Among them, the progress in the field of heat transfer deserves our attention because of its huge industrial value. Many cooling methods based on liquid metal have been developed to accommodate the urgent needs to solve extreme heat flow problems. In this review, we first give an overview of the uniqueness of liquid metal as an untraditional cooling medium. Then strategies to improve the properties of Ga-based liquid metal are presented. The corresponding basic theory of liquid metal heat transfer is discussed. In the subsequent sections, the applications of liquid metal as a fluid in convective heat transfer will be reviewed in details. Finally, key scientific and technical issues and challenges in liquid metal heat transfer will be pointed out to guide future practices.