We inhabit a perpetually accelerating and increasingly interconnected world, with new ideas, fads, and fashions moving at social-media speed. New policy ideas, especially "ideas that work," are now able to find not only a worldwide audience but also transnational salience in remarkably short order.

Fast Policy is the first systematic treatment of this phenomenon, one that compares processes of policy development across two rapidly moving fields that emerged in the Global South and have quickly been adopted worldwide⎯conditional cash transfers (a social policy program...