The Nazi-Soviet War was the largest and most brutal theatre of the Second World War, fought between two of the most ruthless states ever to exist. Bringing together twenty-four of the most accomplished authors in both German and Soviet history, this Cambridge Companion provides the most authoritative, and yet highly accessible, guide to the conflict. Each chapter examines a key aspect of the war from war planning, the opposing forces and the campaigns to criminality and occupation, alliances, the home fronts and postwar legacies and myth-making. The authors demonstrate that the Nazi-Soviet war was both a conventional clash of arms in which millions of soldiers fought in titanic battles, but also a non-conventional war in which soldiers and security forces murdered countless non-combatants. It was a war of resources, industry, mobilisation, administration, and popular support, with implications that still drive European security debates today.