The environment of a DT fusion reactor is unlike anything previously experienced in fission reactors and the requirements for first wall materials will be quite severe. Considerable emphasis is placed on characterizing the environment for both magnetically and inertially confined plasmas, focusing on what we do and do not know at the present time. Once the neutron, photon, and charged particle fluxes are determined, the primary damage functions are calculated and it is shown that the displacement rate in inertial confinement fusion reactors and the helium production rate in all DT fusion reactors are sufficiently different to warrant concern over extrapolation from present facilities. Finally, the major responses of the first wall to the primary damage state appear in the swelling and embrittlement problems. Observations on potential materials and their operating limits are also made.