The study of effective interface models has been quite active recently, with a particular emphasis on the effect of various external potentials (wall, pinning potential,...) leading to localization/delocalization transitions. I review some of the results that have been obtained. In particular, I discuss pinning by a local potential, entropic repulsion and the (pre)wetting transition, both for models with continuous and discrete heights. This text is based on lecture notes for a mini-course given during the workshop "Topics in Random Interfaces and Directed Polymers" held in Leipzig, September 12-17 2005.