  We construct rigidly supersymmetric bulk-plus-boundary actions, both in
$x$-space and in superspace. For each standard supersymmetric bulk action a
minimal supersymmetric bulk-plus-boundary action follows from an extended $F$-
or $D$-term formula. Additional separately supersymmetric boundary actions can
be systematically constructed using co-dimension one multiplets (boundary
superfields). We also discuss the orbit of boundary conditions which follow
from the Euler-Lagrange variational principle.
