This study examines two widely researched attitudes of union members-satisfaction with and commitment to their union-using 1987-88 data on 1,675 union members in professional occupations in Sweden and 476 blue- and white-collar union members in Canada. The authors find, first, that union commitment and union satisfaction are theoretically and empirically different constructs. Second, tests of a theoretical model of union attitude formation indicate that different (though overlapping) sets of factors influence union commitment and union satisfaction. One finding is that activities and processes that provide members with greater information about the union, such as new member orientation programs, newsletters sent to members' homes, and participation in union activities, effectively promote union commitment, but not union satisfaction. The results are very similar across the two samples, suggesting that they have cross-cultural generalizability.