If we try to better understand human motives and the society, it becomes necessary to replace the conventional two-sector (market-government) social model with a more general and theoretically superior social model, the "three-sector model" consisting of market-government-nonprofit sectors. This book demonstrates the validity of this new view by utilizing basic principles of economic policy and social welfare analyses. Moreover, the book has introduced a newly developing practical philosophy in Japan over the last 50 years to achieve both individual wellbeing and better human society.