Societies in all countries are split by major divisions - or 'faultlines' - caused by differences in race, religion, ethnicity, wealth, class or power. Like geological faultlines, some are plainly evident, whereas others are more concealed and can erupt with little warning. Violence along faultlines within states, from Sudan to Iraq to the Congo, is the spark of much contemporary conflict. It has cost millions of lives in the past twenty years alone. In extreme cases, this violence threatens to tear states apart. Yet some countries such as Canada, South Africa and Northern Ireland, have largely succeeded in managing their faultlines. _On the Faultline_ is based on a unique year-long project by some of the world's leading experts to examine the nature of conflict around these divisions. In a world facing acute environmental, migration and resource challenges that can only exacerbate differences, it is an essential guide to understanding a phenomenon that all countries must grapple with in the 21st century.