  A transgression form is proposed as lagrangian for a gauge field theory. The
construction is first carried out for an arbitrary Lie Algebra g and then
specialized to some particular cases. We exhibit the action, discuss its
symmetries, write down the equations of motion and the boundary conditions that
follow from it, and finally compute conserved charges. We also present a
method, based on the iterative use of the Extended Cartan Homotopy Formula,
which allows one to (i) systematically split the lagrangian in order to
appropriately reflect the subspaces structure of the gauge algebra, and (ii)
separate the lagrangian in bulk and boundary contributions. Chern--Simons
Gravity and Supergravity are then used as examples to illustrate the method. In
the end we discuss some further theoretical implications that arise naturally
from the mathematical structure being considered.
