This review article presents an overview of some of the tools, techniques and applications of numerical simulation for integrated microfluidic devices. Provided is a broad overview of the different areas to which numerical techniques have been applied in the development of these devices from detailed studies of fundamental microfluidic problems (e.g., species mixing and sample dispersion) to unique approaches that take a more global overview of the entire system. While the majority of the work to date has been in these areas, also reviewed is some recent progress into other equally important areas of microscale transport such as thermal analysis and chemical reactivity and specificity. An overview of the advantages and disadvantages of common numerical techniques is also presented along with a brief discussion of some of the existing numerical tools, focusing on those best suited for microscale transport analysis. As microfluidic devices become increasingly complex, optimal fluidic and transport designs become more and more difficult to do experimentally. Thus, it is believed that future demand in the field will be for highly integrated simulation tools that allow users without a significant computational fluids background to ‘‘numerical prototype’’ highly integrated devices.