An appropriate boundary treatment is one of the most important tasks to perform when carrying out numerical simulations. The technique to define the boundary condition depends strongly on both the numerical scheme and the type of differential equation to be solved. In terms of implementation effort and cost of computational resources, every boundary should be treated locally in both space and time. In this chapter we discuss techniques to deal with adiabatic walls in the framework of high-order discontinuous Galerkin methods for compressible flow.