This research builds further on the existing conceptual framework of the relationship between decentralization and service delivery and provides a cross-country empirical examination of the core dimensions of decentralization reform on access to two key services: health care and improved drinking water sources. The regression results provide evidence supporting positive and significant effects of fiscal, administrative, and political decentralization, individually, on the variables used to measure access to health care, and improved water provision; although the size and robustness of such effects varies for each dimension of decentralization in relation to each service examined. The results obtained in this study suggest that there is an additional (or "extra") positive effect coming from the interaction of two decentralization dimensions on access to health care and water services (that is, a mutually-reinforcing effect additional to the individual effect of each dimension of decentralization). The results obtained also support the expectation that developing countries could benefit significantly more from decentralization reforms compared to developed countries. These findings underscore the importance of considering all dimensions of the decentralization process when investigating the effects of this reform on any economic, institutional, or social variable. The policy implications are highly relevant, particularly for developing countries: decentralization implemented only through one dimension may render fewer positive fruits in terms of access to services than a multi-dimensional approach. Moreover, learning more about the most beneficial mutually-reinforcing effects across dimensions of decentralization may also help strategically in how the overall decentralization reform is designed.