The study we propose will investigate the function of social norms in cooperation. Two possible functions of norm adherence are discussed. (1) Social norm adherence can signal an individual’s group membership, indicating their similarity in behaviour to group members around them. (2) An individual’s norm adherence might also signal their overall tendency for cooperative behaviour. Though both signals of adherence to social norms are plausible, the proposed study aims to tease them and their effects in intergroup cooperation apart. We do this by studying how the perception of an ingroup or outgroup person violating or adhering to a norm affects cooperation with that person. If norm adherence signals group membership, ingroup bias in cooperation would disappear under norm violation, whereas if group membership signals cooperative intent, ingroup bias in cooperation would persist under norm violation. We will ask participants to read vignettes (short stories) in which we will manipulate both the group membership and norm adherence of an imagined cooperation partner. The participant will next be asked to play a dictator game with this imagined other, meaning they will decide how many of 10 tokens to share with them. The amount of tokens they decide to share will be used as an indication of cooperation. We will be submitting this study as a registered report – any suggestions for improvement are very welcome!