This article analyzes voters for Radical Left Parties (RLPs) in three countries—Germany, the Netherlands, and Sweden. Belonging to the democratic socialist subtype of RLPs, parties in these countries find themselves in an intense “sibling rivalry” with social democratic and green parties for voters on the left side of the political spectrum. There is little existing scholarly analysis of the demand-side of RLPs in competition with their competitors. We fill this gap using the European Social Survey (ESS), testing various demographic and attitudinal variables to disentangle the vote on the left. We conclude that what distinguishes the RLP voter from the social democratic or green voter in these countries is not socio-demographic characteristics but rather three attitudinal variables - satisfaction with democracy, attitudes toward immigrants, and the role of government in reducing income disparities. Furthermore, we find that given these three attitudinal variables, the probability to vote for an RLP compared to a social democratic or green party increases dramatically the farther the voter places him/herself to the left.