Since the 1990s it became increasingly clear that boundary plasmas play a major role in magnetic fusion experiments, and strongly relate to and even dominate central plasma processes. On the one hand, the conditions of the boundary plasma are crucial to obtain high fusion triple products; on the other hand, plasma-surface interactions, a sufficiently low impurity concentration in the fusion volume, heat removal and helium exhaust which directly relate to the boundary plasma, have emerged as equally important goals, and even more difficult to reach in the state of self-sustained thermonuclear burn. Successful resolution of these issues is critical to establish the viability of the tokamak confinement concept as a fusion power reactor.