[en] The quantum formalism of soliton scattering is presented using the path integral collective coordinate method. Constructing the asymptotic states a general method is developed leading to a perturbation expansion about the ground state of an effective multi-soliton sector Hamiltonian. This is discussed explicitly on the two-soliton sector example of sine-Gordon theory where exact multisoliton classical solutions are known. As the first approximation in this perturbation expansion the classical phase shifts found earlier by other authors using different methods are obtained. Next, the first quantum corrections to these classical phase shifts are calculated. The result is found to be in precise agreement with the conjectured exact soliton-antisoliton scattering amplitude of Faddeev, Kulish and Korepin. It also gives further support to the statement of Dashen, Hasslacher and Neveu that for sine-Gordon theory, the semi-classical WKB method gives exact results. (Auth.)