Comparative literature on institutional reforms in multi-level systems proceeds from a global trend towards the decentralization of state functions. However, there is only scarce knowledge about the impact that decentralization has had, in particular, upon the sub-central governments involved. How does it affect regional and local governments? Do these reforms also have unintended outcomes on the sub-central level and how can this be explained? This article aims to develop a conceptual framework to assess the impacts of decentralization on the sub-central level from a comparative and policy-oriented perspective. This framework is intended to outline the major patterns and models of decentralization and the theoretical assumptions regarding de-/re-centralization impacts, as well as pertinent cross-country approaches meant to evaluate and compare institutional reforms. It will also serve as an analytical guideline and a structural basis for all the country-related articles in this Special Issue. Points for practitioners Decentralization reforms are approved as having a key role to play in the attainment of ‘good governance’. Yet, there is also the enticement on the part of state governments to offload an ever-increasing amount of responsibilities to, and overtask, local levels of government, which can lead to increasing performance disparities within local sub-state jurisdictions. Against this background, the article provides a conceptual framework to assess reform impacts from a comparative perspective. The analytical framework can be used by practitioners to support their decisions about new decentralization strategies or necessary adjustments regarding ongoing reform measures.