Imperfectness of magnetic confinement in tokamak devices leads to interactions of plasma particles and radiation with the first walls and plasma facing components of fusion reactors. The most important processes are discussed. Special emphasis is given to the implantation and transport of hydrogen isotopes in solid materials.

One of the main concerns of hydrogen-material interaction is the determination of hydrogen recycling from the inner surface of the first wall, of hydrogen inventory in and hydrogen permeation through the wall of a fusion reactor. Numerical codes have been developed to calculate these properties. Hydrogen-material interaction parameters which are code input data are discussed. Some results of hydrogen isotopes inventory, recycling and permeation calculations in the next step fusion reactor ITER are presented, their accuracy is affected by the availability of data on trapping and surface processes.