The Trojan Horse method is a powerful indirect technique that provides information to determine astrophysical factors for binary rearrangement processes x+ A→ b+ B at astrophysically relevant energies by measuring the cross section for the Trojan Horse reaction a+ A→ y+ b+ B in quasi-free kinematics. We present the theory of the Trojan Horse method for resonant binary subreactions based on the half-off-energy-shell R matrix approach which takes into account the off-energy-shell effects and initial and final state interactions.