The holistic thesis developed by Pierre Duhem challenges the idea that our evidence can conclusively falsify a theory. Given that no scientific theory is tested in isolation, a negative experiment can always be attributed to components other than the theory we test – to the auxiliary hypotheses and background assumptions. How do scientists decide whether the experimental result undermines the theory or points at an error in the underlying assumptions? Duhem argues that we cannot offer a rule that directs when the scientist should employ a radical or conservative strategy in light of a negative result, and ultimately they will appeal to their intuition. More recently philosophers have offered a number of strategies of how to locate error and justify the abandonment of a theory or an auxiliary hypothesis. This Element analyses Duhem's response to holism and subsequent accounts of how the problem can be resolved.