Abstract
The author reviews the thermodynamic and structural behaviour of interfaces between two coexisting phases in 3D. In particular the authors looks at fluid-fluid interfaces in ternary systems. The (microscopic) interface between two phases may (under some circumstances) exhibit structural changes that will drastically change the thickness of the transition region. Examples of these are wetting transitions. Here, the author reviews theoretical as well as experimental results for wetting transitions in binary and ternary (surfactant) mixtures.