This 6 hours lecture is an overview on microfluidics and on the dynamics of fluid interfaces at small scales where surface tension has a leading influence. We will present the various models from particles to continuum approaches and hydrodynamic limits studies, as well as numerical methods for gas and fluids (DSMC, LBM, MD, DPD). As an illustration, we will talk about wall laws for liquids. We will then explore the dynamics of droplets at the microscale, which is of interest in life sciences. Numerical difficulties will be described and Level Set methods for evolving interfaces will be emphasized to treat these kind of problems.