**Preface to "Analysis, Design and Fabrication of Micromixers, Volume II"**

Micromixers are an important component in micrototal analysis systems and lab-on-a-chip platforms which are widely used for sample preparation and analysis, drug delivery, and biological and chemical synthesis. The successful operation of microfluidic devices requires fast and adequate mixing, but mixing is a challenging task due to the laminar feature of the flow at the microscale. Mixing in laminar flows relies on diffusion and requires a longer channel to achieve complete mixing due to the slow process compared to that in turbulent flows. Hence, it is crucial to overcome this challenge to improve the mixing performance. Based on their mixing mechanism, micromixers are classified into two types: active and passive. Passive micromixers are easy to fabricate and generally use geometry modification to cause chaotic advection or lamination to promote the mixing of fluid samples, unlike active micromixers, which use moving parts or some external agitation/energy for the mixing. This reprint covers new mechanisms, numerical and/or experimental mixing analysis, design, and fabrication of various micromixers, which were reported by the Special Issue 'Analysis, Design and Fabrication of Micromixers II' published in *Micromachines*.

> **Kwang-Yong Kim** *Editor*
