This book highlights a major advance in low-energy scattering theory: the Multi-Channel Algebraic Scattering (MCAS) theory, which represents an attempt to unify structure and reaction theory. It solves the Lippmann-Schwinger equations for low-energy nucleon-nucleus and alpha-nucleus scattering in momentum space, allowing both the bound and scattering states in the compound nucleus formed to be described. Results of various cases are presented and discussed.