  A relativistic formulation of reaction theory for nuclei with a dynamics
given by a unitary representations of the Poincar\'e group is developed.
Relativistic dynamics is introduced by starting from a relativistic theory of
free particles to which rotationally invariant interactions are added to the
invariant mass operator. Poincar\'e invariance is realized by requiring that
simultaneous eigenstates of the mass and spin transform as irreducible
representations of the Poincar\'e group. A relativistic formulation of
scattering theory is presented and approximations emphasizing dominant degrees
of freedom that preserve unitarity, exact Poincar\'e invariance and exchange
symmetry are discussed. A Poincar\'e invariant formulation of a (d,p) reaction
as a three-body problem is given as an explicit example.
