Motivational models suggest that individuals use substances to achieve desired effects. Given different pharmacological effects across drug classes, and variations in social context, one would expect that the motives instigating use differ by drug class. However, commonalties in motives across drugs have also been observed. The purpose of this study was to examine similarities and differences across a common set of motives for alcohol and marijuana among experienced users of both drugs. Participants were 46 college students (21 women) who completed a motives assessment twice, once for marijuana and once for alcohol. All had used each drug 60 or more times in their lifetime. Social motives were more highly endorsed for alcohol than marijuana. Expansion motives were more highly endorsed for marijuana. Enhancement motives were more highly endorsed for marijuana than alcohol among women but not men. Endorsement of coping and conformity motives did not differ across drugs. Experienced users of marijuana and alcohol discriminate between their reasons for using the two drugs. These findings are discussed with regard to the differentiation between and commonalties among substances of abuse.