This thesis examined the condit:,ns under which assimilative and contrastive responses would be observed foHowing ingroup and outgroup targets. Eight experiments tested whether diverging cognitive, behavioural, and emotional responses to group primes would be evident for perceivers who reported different levels of commitment to their ingroup. Specifically, it is argued that the level of commitment the perceiver has to a social group to which they belong, i.e., their level of ingroup identification, may moderate their responses to outgroup primes. It was predicted that higher identifiers would differentiate the ingroup from the outgroup by contrasting their responses away from an outgroup prime, while lower identifiers would not be motivated to contrast from group primes but should assimilate to both ingroup and outgroup primes. In the first part of the thesis these predictions were supported across four experiments using various priming methodologies and dependent measures. Lower identifiers showed some evidence of assimilation to both ingroup and outgroup primes while higher identifiers consistently demonstrated contrastive responses from outgroup primes. In the second part of the thesis the processes underlying outgroup contrast effects for higher identifiers were investigated. Findings from two experiments supported the observation from the social comparison literature that activation of the personal self co-varies with contrastive responses. Further examination revealed that the activation of the social self was associated with contrastive responses suggesting that self-categorisation processes may be involved in outgroup contrast. The implications of these findings for the processes underlying social judgments, automatic behaviour, and Social Identity Theory are discussed.