Meso/Micro structured flow devices have a wide range of applications as mixers or reactors for continuous analytical chemistry, high-throughput production and product formulation, and biological and microbiological analysis systems, among others They are of particular interest for applications that fit the lab-on-a-chip concept, requiring the handling of small volumes (10-9 to 10-6 litres) and a high level of portability. Mixing operations in these devices often occur in the laminar regime, at quite low Reynolds numbers, due to small flow rates. Notwithstanding the devices' small dimensions (mm to µm), molecular diffusion itself may not be relied upon to completely homogenise the feeding streams in attractive flow times and reactor lengths, especially when blending of highly viscous fluids or fast reactions are involved in the process. The key for efficient mixing relies on the capacity to promote, by advective mechanisms, a fast distribution of the fluids in the cross section of the device's channel and a fast growth of the intermaterial surface area. In this presentation different types of meso and micro flow devices geometries, mixing mechanisms and mixing quantification variables will be described. Focus will then be given to mixing by confined impinging jets mixers in a laminar chaotic flow regime.