The VKI Lecture Series on "Large eddy simulation and related techniques, theory and application " will take place at the von Karman Institute for Fluid Dynamics (Belgium) in February 22-26, 2010. The purpose of this Lecture Series is to offer a full overview of the present development and the potential of the Large Eddy Simulation (LES) of turbulent flows. The first part of the course will introduce and discuss fundamental principles, present state-of-the-art applications and possible developments of LES and Detached Eddy Simulation (DES) which represents the most promising technique to extend the usefulness of LES for high Reynolds-number flows.