A growth surge in the world’s largest economy could provide a significant boost to global activity. In contrast, uncertainty about the direction of US policies could have the opposite effect. This column investigates spillover channels linking the US and the global economy. An acceleration in US growth would have positive effects for the rest of the world if not counterbalanced by increased trade barriers. However, policy uncertainty could hamper global growth, and could have particularly bad effects on investment growth in emerging and developing economies.