The colloquium will be devoted to presenting advances in the mechanics of unsaturated porous media, in general, and soils, in particular. The principle of effective stress and its extension from the saturated to unsaturated porous media has been the subject of much research, but there is no consensus in this regard. Various approaches have been used to get insights into this principle. They span form micromechanical approaches to thermodynamic investigations. As it is evident from the title, the colloquium will be mostly centered on the concept of effective stress in unsaturated porous media and recent advancements of underlying theories.