The growth of the non-profit, voluntary or third sector has been widely recognized throughout the world. This text seeks to provide a definition and a common classification of the non-profit sector, while recognizing the great diversity of voluntarism internationally. The remainder of the text is devoted to country-by-country definitions of the sector in 13 representative states from the developed, developing and post-socialist worlds. Among the countries covered USA, UK, France, Germany, Japan, India, Brazil, Egypt and Hungary. The study demonstrates that the division of societies into public and private is too simplistic, and that a third sector with its own characteristic features and dynamics has already emerged as a powerful force in the global economy.