Introducing charity as a social principle valid not only for the micro-relationships like the family or friendship but also for the macro-relationships like the economy or politics, poses a challenge, because charity, as the central message of the Gospel and the distinguishing Christian virtue, is not a directly applicable social program. It requires the mediation both of a correct political philosophy and of a social organization based on legal justice. However, charity is difficult to handle in organizations because the exigencies of charity go beyond justice and are difficult to predict. Love (charity, benevolence, etc.) gives without return, without calculation. Love transcends the loving person and therefore cannot be forced into a socio-legal structure that needs regularity and predictability in order to function. This then is the challenge for Christians striving to evangelize the society in general and the economy in particular: Charity is the hallmark of Christian ethics, but is not fit to function as an immediately applicable social principle. Christians therefore struggle to find the way that charity can manifest itself institutionally in a free market economy. This book is a result of such an endeavor. We ask in which way the big social principles of human dignity, solidarity and subsidiarity as they have been developed in centuries of Catholic social thought and magisterial teaching express charity as a principle in society, and how solidarity is compatible with freedom and spontaneity.