This book presents the results of a research project Innovative Social Investment: Strengthening Communities in Europe (InnoSI) nr 649189, financed by the European Commission in the frames of Horizon 2020 Programme. The research work carried out under this project conducted in 2015-2017 covered many stages: desk research, through defining the institutional, financial and political social investments in selected European countries, constructing indicators of their measurement, identification of innovative investment solutions at the local level and regional studies in Europe, analysis of selected case studies, till attempting to forecast future scenarios for the development of social investments based on the foresight method. The outlined assumptions of the investment paradigm and the controversies appearing around this concept point to the relevance of the issue and the great interest in social investments both in the scientific and practical aspects. These two areas - theory and practice - are combined in this monograph. It presents the investment approach in public policies in the European Union, with particular emphasis on the Polish context of solutions and investment activities undertaken in practice. On the conceptual and methodological level, the considerations taken up in the book are based on the theory of change, which presents preliminary assumptions and key actions to implement effective and efficient public intervention. The theory of change is applied to the analysis the social investment. Rządowy Program na rzecz Aktywności Społecznej Osób Starszych (Government Program for the Elderly Social Activity, ASOS) was presented as an example of the innovative social investment created at national and implemented at local level in Poland.