Cross-national research is an absolute necessity if we are to understand contemporary human societies in general and the role of religion in particular. To be useful, comparative survey research needs to meet high scientific standards of reliability and validity and achieve functional equivalence across surveys. This chapter examines how well-designed and well-executed cross-national/cultural survey research can best minimize error and maximize equivalence. The chapter first introduces the concept of total survey error (TSE), including interactions among the error components, its application when multiple surveys are involved, and comparison error across cross-national surveys. Second, obtaining functional equivalence and similarity in cross-national surveys is discussed. Third, the challenges of doing cross-national surveys are considered, as well as how combining traditional approaches for maximizing functional equivalence with the utilization of TSE can minimize comparison error and maximize comparative reliability and validity. Fourth, attention is given to minimizing comparison error in question wordings in general. Special attention is given to dealing with differences in language, structure, and culture. Lastly, specific issues relating to studying religion cross-nationally are examined.