Abstract. If we wish to implement dialogue systems which express emotion, dialogue corpora annotated for emotion would be a valuable resource. In order to develop such corpora we require a reliable annotation scheme. Here we describe an annotation scheme for emotion in dialogue using categorical labels to complement previous work using dimensional scales. The most difficult challenge in developing such a scheme is selecting the categories of emotions that will yield the most expressive yet reliable scheme. We apply a novel approach, using a genetic algorithm to identify the appropriate categories. There is increasing recognition of a need to incorporate an understanding of emotion into dialogue systems, since this understanding can greatly enhance their performance. For example, artificial communicative agents can be made to converse more naturally and appear more engaging by having characters behave emotionally [1, 2]. For gaining an understanding of the relationship between emotion ...