Microfluidic is a powerful and emerging technology for management of liquid sample at micro scale. It is now widely used for biological application and diagnostic. Nanoliter droplets of uniform size spontaneously form in microchannels when two immiscible fluid streams merge. This nonlinear process involves basic physics. This results in droplets of sizes comparable to the channel diameter. We will first introduce some related basic questions for multiphase flow at micro scale: geometry, wetting, diffusion, instabilities, and then discuss how to take advantage of this physics for efficient regulation of droplet traffic in microfluidic devices. This new route for easy and steady production of calibrated emulsions and traffic control of the droplets open a stimulating field for application of microfluidic devices. These tiny droplets are almost ideal as chemical reactors for synthesis and for formulation and management of complex fluids. Useful applications are: micro-rheology, micro calorimeter, liquid liquid phase transfer, crystallization, phase diagram, micro reactors… One could also see the main advantage of formulation and synthesis on a chip if evaluation of the product is integrated and is a seam less process. It is then worth to discuss which analytical tool are available and what should be develop to run some real life formulation experiment on a chip form A to Z.