The absorption and emission properties of a hot bounded plasma can be greatly influenced by collective behavior in the plasma. A homogeneous slab model of a collisionless plasma is used in a theoretical study of these collective effects. Peaks in the absorptivity occur at the resonance frequencies of longitudinal standing waves in the plasma. Power can be absorbed from an incident electromagnetic wave by Landau damping of the plasma waves which it couples to. Radiation is emitted from a collisionless bounded plasma because plasma waves excited in the wakes of fast electrons are partially converted to electromagnetic waves at the plasma boundaries. The radiation has peaks at the same frequencies as the absorption because of the collective reinforcement of the plasma waves at their resonance frequencies. In thermal equilibrium the collisionless absorption and emission obey Kirchhoff's law. The emission may be enhanced if many nonthermal electrons are present.