As Hammond has argued, traditional explanations for disagreement among experts (incompetence, venality, and ideology) are inadequate. The character and fallibilities of the human judgement process itself lead to persistent disagreements even among competent, honest, and disinterested experts. Social Judgement Theory provides powerful methods for analysing such judgementally based disagreements when the experts' judgement processes can be represented by additive models involving the same cues. However, the validity and usefulness of such representations depend on several conditions: (a) experts must agree on (...) a problem definition, (b) experts must have access to the same information, and (c) experts must use the same organising principles. When these conditions are not met, methods for diagnosing and treating disagreement are poorly understood. As a start towards developing such an understanding, sources of expert disagreement are discussed and categorised. (shrink)