This paper explores the theoretical issues and the empirical literature regarding the selectivity of migrants. Although the primary focus is on international migration, reference is made to internal migration and return migration. The theoretical analysis indicates a tendency toward the favorable self-selection (supply) of migrants for labor market success. The favorable selectivity is more intense the greater the out-of-pocket (direct) costs of migration and return migration, the greater the effect of the higher level of ability on lowering the costs of migration, and the smaller the relative skill differentials in the lower-wage origin relative to the higher-wage destination. Favorable selectivity for labor market success can be expected to be less intense for non-economic migrants, such as refugees, tied movers and ideological migrants, and for sojourners (short-term migrants) and illegal aliens. Among countries for whom entry restrictions are binding, the criteria for rationing immigration visas (demand) will influence the favorable selectivity of those who actually immigrate. Selection criteria can ration visas on one or more characteristics that enhance labor market earnings (e.g., education), or on characteristics that are seemingly independent of skill level (e.g., kinship ties). Under either criteria there will be a tendency for immigrants to be favorably selected, although this is less intense under the later criteria. The overall favorable selectivity of immigrants, therefore, depends on the favorable selectivity of the supply of immigrants and the criteria used to ration admissions.