We present a theory on migration of dual-earner couples and test it in the context of international migration. Our model predicts that the probability that a couple emigrates increases in the home-country earnings of the primary earner. The effect of the home-country earnings of the secondary earner may go either way. We test our theory using population-wide Danish administrative data from 1982 to 2010. We analyze migration decisions separately for couples in which men earned more and couples in which women earned more. The empirical results for dual-earner couples are in line with the theory. The elasticity of the probability of emigration with respect to the primary earner's income is very large. When analyzing emigration for 5 or more years the elasticity of the probability of emigration varies between 1.6 and 3.6 for groups with female primary earner and between 2.4 and 3.1 for groups with male primary earner. The elasticity with respect to the secondary earner's income varies in sign and is generally small. Primary earners in couples are more strongly self-selected with respect to their income than singles. This is a novel result that runs against the intuition that family ties weaken self-selection. Secondary earners in couples, on the other hand, are more weakly self-selected with respect to their income than singles. College education of either partner makes couples more, and having children makes couples less mobile. Power couples are most likely to emigrate, but also most likely to return.