This paper considers a class of fluidic devices, anticipated to become important in the near future, where characteristic channel dimensions are in the range 0.1 to 1.0 microns. Typical current applications of microfluidics have device sizes of 10 to 100 micron, this is sufficiently small to force laminar flow but not so small that molecular diffusion is a dominant factor. In the smaller devices contemplated here, diffusion is important and existing mixing strategies and correlations are no longer applicable. Novel results and interesting complexities are discussed for reactive, single and two phase flows in sub-micron channels.