In every cross-cultural study, the question as to whether test scores obtained in different cultural populations can be interpreted in the same way across these populations has to be dealt with. Bias and equivalence have become the common terms to refer to the issue. Taxonomy of both bias and equivalence is presented. Bias can be engendered by the theoretical construct (construct bias), the method such as the form of test administration (method bias), and the item content (item bias). Equivalence refers to the measurement level at which scores can be compared across cultures. Three levels of equivalence are possible: the same construct is measured in each cultural group but the functional form of the relationship between scores obtained in various groups is unknown (structural equivalence), scores have the same measurement unit across populations but have different origins (measurement unit equivalence), and scores have the same measurement unit and origin in all populations (full scale equivalence). The most frequently encountered sources of bias and their remedies are described.