Focusing on the realities of post-communist Romania and Poland, this thesis inquires one thought-provoking puzzle characterizing the re-building process of post-communist civil societies: the impressive numerical growth of NGOs. The aim of the paper is to address two interrelated questions. First, what is the organizational/structural outcome of this phenomenon of “mushrooming NGOs”? And, second, does foreign financial assistance offer a fully satisfactory causal explanation for this numerical growth? Employing a comparative perspective and founding its research mainly on a qualitative analysis of official data, reports and secondary sources, the present thesis argues that in both countries the numerical growth of NGOs led to the creation of a similar structuring of the nonprofit sector in terms of types, numerical significance and regional distribution of NGOs. Second, the present study argues that when evaluated from both a quantitative and qualitative perspective, Western financial aid offers only a partial explanation for the development of the NGO sector. In both its theoretical framework and empirical analysis, the thesis indicates several factors explaining why foreign aid does not provide a fully satisfactory explanatory framework for the numerical growth of NGOs, like for example the lack of knowledge on the part of the donor community about local realities, an unequal distribution of funds among NGOs and a fluctuating flux of aid. In its concluding part, the thesis proposes alternative explanatory variables under the heading of guidelines for further research.