The cover picture showsa new three dimensional micromixer which consists of two layers of spiral channels overlapped together in the vertical direction. Based on the principle of Dean effects, the topological structure is beneficial to produce, enhance and sustain the Dean vortices, which can perturb the laminar fluid effectively. The detailed parameters have been optimized by using the computational fluid dynamics software. The results indicate that the erect channel which is connected with the two layers of spiral channels plays a critical role for well mixing. Meanwhile, the effect of mixing has been identified in a fabricated glass-micromixer and the mixing ef?ciency of 90% has been achieved. This micromixer has manifested high mixing efficiency and presents good practicability in the versatile microfluidic systems. More details are discussed in the article by Qi et al. on page 209–214.