Bias and equivalence are key concepts in the methodology of cross-cultural studies. Bias is a generic term for any challenge of the comparability of cross-cultural data; bias leads to invalid conclusions. The demonstration of equivalence (lack of bias) is a prerequisite for any cross-cultural comparison. we first describe considerations that are relevant when choosing instruments in a cross-cultural study, notably the question of whether an existing or new instrument is to be preferred.We then describe the definition, manifestation, and sources of three types of bias (construct, method, and item bias), and three levels of equivalence (construct, measurement unit, and full score equivalence). We provide strategies to minimize bias and achieve equivalence that apply either to the design, implementation, or statistical analysis phase of a study. The need to integrate these strategies in cross-cultural studies is emphasized so as to increase the validity of conclusions regarding cross-cultural similarities and differences and rule out alternative explanations of cross-cultural differences.