Although widely employed in the literature, the concept of party institutionalization has often been poorly and ambiguously defined: sometimes the term has been simply used without further explanation, sometimes the notion has been equated with that of party system institutionalization. Taking as a starting point the idea that such conceptual ambiguity is problematic for both social science research and, especially, causal analysis, in this paper I try to unpick some of the conceptual confusion that has resulted from this conflation. The idea is to examine the numerous accounts of institutionalization employed in the study of political parties, exploring what are their main dimensions of the notion and in which way have they been operationalized. After that, and taking into consideration the results of such theoretical analysis, I will advance a conceptual and analytical framework which, distinguishing between (social) rootedness and (organizational) systemness as the main dimensions of the notion and employing several indicators (e.g. membership, nationalization, splits and mergers, unity, etc.) to measure the level of party institutionalization, is considered to be more accurate (both in terms of validity and reliability) when trying to build a realistic examination of the topic. Finally, and on the basis of what can be observed in the process of party formation and development in new post-communist democracies, the paper attempts to answer the following questions: Are Eastern European political parties institutionalized? And, if so, are they evenly so? Moreover, are social rootedness and organizational stability always mutually compatible?
