  We review the construction and applications of exactly Poincar\'e invariant
quantum mechanical models of few-degree of freedom systems. We discuss the
construction of dynamical representations of the Poincar\'e group on
few-particle Hilbert spaces, the relation to quantum field theory, the
formulation of cluster properties, and practical considerations related to the
construction of realistic interactions and the solution of the dynamical
equations. Selected applications illustrate the utility of this approach.
