Chapter 19 concludes the book and analyzes the importance of the notion of synthesis for Tinbergen. Synthesis for him was a unity in moral and scientific perspective, and he admired most those economists and social reformers who were able to combine scientific insight with moral vision and practical action. The chapter analyzes the extent to which Tinbergen’s own work and efforts represent such a synthesis. It is suggested that his personal goals of peace and harmony were only partially integrated with his scientific economics. These elements coexisted, which meant that he left a fragmented legacy. His contributions to scientific expertise and its institutionalization, however, had the most long-lasting influence. And although expertise proved hard to combine with his own high-minded idealism, it is demonstrated that what attracted economists like Tinbergen to a role as policy expert was precisely the belief that social goals could be pursued through economic policy. The goal for control through rational planning of economic policy also fitted his personality well, and thus best captures the Tinbergen synthesis.