Elements of relativistic quantum mechanics for final state interactions

In the baryon resonance region the likelihood that electroproduction reactions will lead to multiple hadron production either in the final-state or in intermediate states requires-a framework capable of describing the non-perturbative, coupled-channels nature of hadron scattering. For applications in the energy region accessible to the Thomas Jefferson National Accelerator Facility, such a framework must be Poincare covariant, electromagnetic gauge invariant and unitary. These aspects of final-state interactions and how they have been implemented into frameworks based on the instant-form of relativistic quantum mechanics are briefly outlined.