The new reaction-diffusion code FACE (First wAll simulation CodE) is developed for modeling plasma-material–interaction processes taking place in the first wall of fusion devices. The code simulates implantation, desorption, transport, and interaction of an arbitrary number of particle and quasi-particle species, such as dissolved gases and intrinsic or induced defects, in a wall material. It allows descriptive and predictive modeling of retention and outgassing of plasma constituents in plasma-exposed materials for analysis of experimental data and assessment of performance of plasma-facing components under various static and transient plasma conditions. The physical model, capabilities, future development, and example applications of the code are presented.