In contrast to everyday use of the term discrimination, we propose that discrimination can be appraised as either illegitimate or legitimate, and a comprehensive analysis of responses to discrimination needs to account for both ways of experiencing discrimination. We examine how perceived pervasiveness of discrimination and legitimacy appraisals affect group commitment among women in academia (Study 1) and tobacco smokers facing an upcoming smoking ban (Study 2). We found support for our hypothesis that legitimacy of discrimination appraisals moderates the effect of pervasiveness of discrimination. In both studies, group identification and collective action intentions were undermined most when the ingroup claimed that discrimination against them was legitimate and discrimination was perceived as pervasive. In both studies, group identification mediated the effects on collective action intentions. The results highlight the important role of legitimacy appraisals in understanding disadvantaged group members' responses to discriminatory treatment. Copyright © 2010 John Wiley & Sons, Ltd.