  A wide class of boundary problems in quantum mechanics is discussed by using
path integrals. This includes motion in half-spaces, radial boxes, rings, and
moving boundaries. As a preparation the formalism for the incorporation of
$\delta$-function perturbations is outlined, which includes the discussion of
multiple $\delta$-function perturbations, $\delta$-function perturbations along
perpendicular lines and planes, and moving $\delta$-function perturbations. The
limiting process, where the strength of the $\delta$-function perturbations
gets infinite repulsive, has the effect of producing impenetrable walls at the
locations of the $\delta$-function perturbations, i.e.\ a consistent
description for boundary problems with Dirichlet boundary-condition emerges.
Several examples illustrate the formalism.
