Crystal defects demand atomistic modeling near defect cores for accuracy and continuum modeling to capture long-range elastic interactions for efficiency. To address this modeling problem, material scientists have proposed a plethora of hybrid atomistic-to-continuum coupling methods. Luskin and his collaborator Ortner have formulated a novel and general numerical analysis of these methods and derived quasi-optimal methods that balance the errors of coupling, continuum approximation, and far field boundary conditions.