Microreaction technology is one of the most innovative and rapid developing fields in chemical engineering, synthesis and process technology. Many expectations toward enhanced product selectivity, yield and purity, improved safety, and access to new products and processes are directed to the microreaction technology. Microfluidic mixer is the most important component in microfluidic devices. Based on various principles, active and passive micromixers have been designed and investigated. This review is focused on the recent developments in microfluidic mixers. An overview of the flow phenomena and mixing characteristics in active and passive micromixers is presented, including the types of physical phenomena and their utilization in micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, T-micromixer is highlighted as an example to illustrate the effect of design and operating parameters on mixing efficiency and fluid flow inside microfluidic mixers. Microreaction technology is one of the most innovative and rapid developing fields in chemical engineering, synthesis and process technology. Many expectations toward enhanced product selectivity, yield and purity, improved safety, and access to new products and processes are directed to the microreaction technology. Microfluidic Based on various principles, active and passive micromixers have been designed and investigated. This review is focused on the recent developments in microfluidic mixers. An overview of the flow phenomena and mixing characteristics in active and passive micromixers is presented, including the types of physical phenomena and their utilization in micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, T-micromixer is highlighted as an example to illustrate the effect of design and operating parameters on mixing efficiency and fluid flow insi de microfluidic mixers.