With the advent of new, high-performance, ground-based and space-borne facilities, the multi-wavelength investigation of massive stars has been boosted over the last decade. It is nowadays possible to study these objects from the radio domain up to the soft gamma-ray energies. The aim of this four and a half day meeting, which will be organized in the well-known series of the Liège astrophysical colloquia, is to bring astrophysicists from different horizons together to discuss how this multi-wavelength approach has revolutionized our view of massive stars and their surroundings in our Galaxy and beyond.