  A general technique is presented for constructing a quantum theory of a
finite number of interacting particles satisfying Poincar\'e invariance,
cluster separability, and the spectral condition. Irreducible representations
and Clebsch-Gordan coefficients of the Poincar\'e group are the central
elements of the construction. A different realization of the dynamics is
obtained for each basis of an irreducible representation of the Poincar\'e
group. Unitary operators that relate the different realizations of the dynamis
are constructed. This technique is distinguished from other solutions of this
problem because it does not depend on the kinematic subgroups of Dirac's forms
of dynamics. Special basis choices lead to kinematic subgroups.
