Globalization has led to increased migration and labor mobility over the past several decades and immigrants generally seek jobs in their new countries. Tests of general mental ability (GMA) are common in personnel selection systems throughout the world. Unfortunately, GMA test scores often display differences between majority groups and ethnic subgroups that may represent a barrier to employment for immigrants. The purpose of this study was to examine differences in GMA based on immigrant status in 29 countries (or jurisdictions of countries) throughout the world using an existing database that employs high-quality measurement and sampling methodologies with large sample sizes. The primary findings were that across countries, non-immigrants (n = 139,464) scored approximately half of a standard deviation (d =.53) higher than first-generation immigrants (n = 22,162) but only one-tenth of a standard deviation (d =.12) higher than second-generation immigrants (n = 6,428). Considerable variability in effect sizes was found across countries as Nordic European and Germanic European countries evidenced the highest non-immigrant/first-generation immigrant mean differences and Anglo countries the smallest. Countries with the lowest income inequality tended to evidence the highest differences in GMA between non-immigrants and first-generation immigrants. Implications for GMA testing as a potential barrier to immigrant employment success and the field's current understanding of group differences in GMA test scores will be discussed.