Evolutionary indeterminists argue that, in addition to any indeterminism introduced by quantum events, at least some evolutionary processes are themselves fundamentally indeterministic. That is, they maintain that the chance element in evolutionary processes results from indeterminism in the processes themselves, rather than simply from our cognitive limitations. Not everyone has been persuaded. A number of philosophers have argued that claims for evolutionary indeterminism are premature at best and deeply confused at worst. They maintain that evolutionary processes can and should be understood as deterministic processes. According to them, “chance” is merely a word denoting our ignorance of causes. This controversy is now one of the liveliest topics in the philosophy of biology. This article reviews the main arguments on each side, showing how the issues at stake in this debate raise fundamental questions about the nature of science as an explanatory enterprise and of the world it seeks to explain.