In order to improve the competitiveness of city regions in the face of radical global economic competition, targets of city governance must exceed administrative boundaries. The complexity of problems in metropolitan areas has also increased. Although many various cross-boundary governance models have been adopted, their effectiveness widely varies. Therefore, an effective cross-boundary governance model is critically needed in planning theory and practice. This study investigated the key factors affecting cross-boundary governance so that a theoretic model can be established to evaluate the effectiveness of various cross-boundary governance models. After reviewing of cross-boundary governance model in United States, Europe and Japan, and performing focus group interviews with central and local government officers and experts in Taiwan, four critical factors of effective cross-boundary governance are identified and named as A+CORP (Agreement + Capital, Organization, Regulation, Plan) model. Furthermore, to measure the explanatory capability of the requirement model, existing cross-boundary cooperation models in Taiwan are evaluated. The analytical results of this study can be used to improve the cross-boundary governance models in practice and theoretical development in the future.