Children of almost any age can break the law, but at what age should children first face the possibility of criminal responsibility for their alleged crimes? This work is the first global analysis of national minimum ages of criminal responsibility (MACRs), the international legal obligations that surround them, and the principal considerations for establishing and implementing respective age limits. Taking an international children's rights approach, with a rich theoretical framework and the vitality of the UN Convention on the Rights of the Child, this work maintains a critical perspective, such as in challenging the assumptions of many children's rights scholars and advocates. Compiling the age limits and statutory sources for all countries, this book explains the broad historical origins behind most of them, identifying the recurring practical challenges that affect every country and providing the first comprehensive evidence that a general principle of international law requires all nations, regardless of their treaty ratifications, to establish respective minimum age limits.