Religiousness and spirituality are important in the study of psychology for several reasons: They are central to identity and values; they have been reported as being positively associated with health and well-being; and they capture (and perhaps lead to) the largest measurable psychological differences between societies. At five items, the Duke University Religion Index (DUREL) is an efficient measure, which advantageously distinguishes between religious sentiment and activity, and between formal versus private involvement. This project extends its internal validation throughout the world, with formal tests of measurement invariance in three languages in Namibia (Study 1) and in a global sample of 26 countries (Study 2). Results confirmed a two-subscale factorial structure of Religious Activity (combining organizational and non-organizational activities) and Intrinsic Religiosity in Namibia and in half of the 26-country samples. In 13 other countries, fit was best for a one-factor model. Fit was problematic where there was too little intra-national variance: in China and Japan, where religious involvement is universally low, and in Tanzania, where it is universally high. Scalar measurement invariance was found for the one-factor structure across 13 samples and for the two-factor structure across 11 samples. External validation of the scale is examined using psychological and sociodemographic variables. This validation of the DUREL supports its use across contexts, facilitating increased attention to this important aspect of both personality and culture.