In this paper, a literature review of the recent research advances and applications of microchannel (from 1 μm to 1 mm) heat exchangers (μHXs) is presented. After a brief introduction of basic definitions, the advantages and limitations of μHXs are summarized with examples. Recent applications of these exchangers are reported. Although much in-depth research work still needs to be done, great potential has already been shown for large-scale applications of μHXs in process intensification of various industrial areas. Moreover, in order to solve the key issue of the link between the micro-scale and the macro-scale, multi-scale methodology such as fractal and constructal approaches for the design optimization of μHXs are introduced. Finally, the concept of constructal heat exchanger is presented.