Two-phase flow and flow boiling phenomena of fluidic mixtures in small and mini channels are becoming important in the miniaturization of thermal systems. This paper aims to present a state-of-the-art review in this important area and to identify what have been done so far and what still need to be done in the future. Firstly, various definitions of small and mini channels are described and the criteria based on these definitions are compared with each other. Comments on different viewpoints of the channel size classifications are acknowledged. Secondly, the background of two-phase flow and flow boiling of mixtures is described. Then, the current research status of two-phase flow and flow boiling of mixtures in normal size channels is presented as it is a basis for the study of two-phase flow and flow boiling of mixtures in small and mini channels. Finally, an overall review of two-phase flow and flow boiling of mixtures in small and mini channels is presented. It is concluded that the available study of two-phase flow and flow boiling of mixtures in small and mini channels is rather scarce and a systematic knowledge of two-phase flow and flow boiling of mixtures in small and mini channels is required. Based on this review, the future research directions including both fundamental and applied research in this area have been indicated. (c) 2005 Elsevier Ltd. All rights reserved.