The emergence and development of argumentation skills in interpersonal conflict situations are the focus of this study. The mental structures used to understand arguments are related to those used to understand social conflict and goal-directed action. The desire to maintain or dissolve a relationship, to persuade, and to understand a position operate throughout interpersonal arguments. Decisions made about whether a relationship should be maintained influence the reasoning and thinking during negotiation, the negotiation strategies, and the outcome of an argument. Because social goals are crucial to understanding argument, negotiations and memory for an argument may be affected as to bias and accuracy. The ability to understand an argument is claimed to emerge early in development. By 3 years of age, children understand and generate the principle components of an argument, either in face-to-face interaction or individual interviews. The ability to construct detailed, coherent rationales in defense of a favored position improves with age. This development, however, does not guarantee a deeper under-standing of one's opponents. The conditions that prevent greater understanding of the opposition from developing are discussed. The ways in which biases and limited understanding can be overcome are also considered.