The interaction of hydrogen isotopes with the inner walls of the plasma vessel is important for the physical, radiological and economical performance of controlled nuclear fusion devices. It can be subdivided into three major areas: (1) recycling phenomena describing the balance of incident and released hydrogen, (2) the development of hydrogen inventory in, and (3) the permeation through the first wall. In a first step, the composition and structure of the wall material must be characterized. It is the surface layer of this material where most interaction processes (trapping, reflection, release and diffusion) are controlled. In a second step, the radiation environment of the first wall must be defined; it can generally not be obtained by simulation experiments. Material composition and radiation environment are responsible for erosion and deposition of surface layers generally incorporating large amounts of hydrogen. IBA is the most important method of first wall analysis because it offers a choice of different analyzing methods in one device. Specific complications arise, however, because profiling of mobile hydrogen requires measurements during exposure; further, detrapping by the analyzing beam may in some hydrogen-containing layers amount to several thousand atoms per ion.