Group members tend to like other members of their own group more than members of groups to which they do not belong. This paper focuses on some of the initial determinants of this own-group preference and on the isolation of factors which increase or decrease it. The major finding appears to be that the mere anticipation of cooperation or competition can affect "own group bias" (OGB). The finding that those subjects in groups anticipating cooperation also showed a significant OGB effect offers further support for the balance theory interpretation that classification as a member of one group along with exclusion from another is sufficient to produce OGB. However, this study does not lend insight into Rabbie and Horwitz's (1969) failure to find OGB as a function of classification along, and their explanation that it may be due to the failure to provide justification for the division into groups remains plausible. (Author/TA)