Ideology and altruism are central to understanding the non-profit charitable sector. This paper addresses three questions. Why do people make charitable gifts? Why do they usually give to non-profit organisations? When can non-profits run by committed ideologues compete with profit-oriented entrepreneurs in the provision of services? the altruistic motives of individuals and the ideological commitments of entrepreneurs come together to support charitable organisations. The non-profit form provides a weak guarantee that gifts are not being syphoned off as profits. Furthermore, independent non-profits can often better reflect donors' desires than public agencies constrained by majoritarian claims, and ideological entrepreneurs can use the non-profit form to reify their beliefs without being accountable to profit-seeking investors. A non-profit organisation can only survive, however, if it can attract money and customers. Sometimes its ideological character will facilitate both tasks. Non-ideological customers may, nevertheless, patronise an ideological non-profit if the entrepreneur's commitment helps to guarantee high quality.