  The goal of this paper is to propose and discuss a practical way to implement
the Dirac algorithm for constrained field models defined on spatial regions
with boundaries. Our method is inspired in the geometric viewpoint developed by
Gotay, Nester, and Hinds (GNH) to deal with singular Hamiltonian systems. We
pay special attention to the specific issues raised by the presence of
boundaries and provide a number of significant examples -among them field
theories related to general relativity- to illustrate the main features of our
approach.
