  The theory of free relativistic fields is shown to arise in a unified manner
from higher-order, configuration-space, irreducible representations of the
Poincar\'e group. A de Sitter subalgebra, in the massive case, and a Poincar\'e
subalgebra, in the massless case, of the enveloping algebra of the Poincar\'e
group are the suitable higher-order polarizations. In particular, a simple
group-theoretic derivation of the Dirac equation is given.
