Demographics on national, regional, and global Pentecostalism provide an essential backdrop to almost every kind of quantitative or qualitative study done on other aspects of Pentecostalism. This article outlines both the history and the research findings related to the subject of defining, categorizing, and counting Pentecostals. Subjects covered include early attempts to count Pentecostals, the development of taxonomies of different types of Pentecostals and Charismatics, and statistical estimates of Pentecostals and Charismatics by type.
Vast efforts are put into the collection of statistics in every country of the world relating to religious adherence. Quantitative tools in the context of demography – births, deaths, conversions, defections, immigration, and emigration – provide a comprehensive view of demographic changes in religious diasporas, which are created by the migration of people worldwide. Utilizing the taxonomies of religions and peoples from the World Christian Database (WCD) and World Religion Database (WRD), a preliminary examination of religious diasporas shows 859 million people (12.5% of the world’s population) from 327 peoples in diasporas around the world. The continuing trend of religious migration around the world is both increasing and intensifying religious diversity, especially in the former Christian West. This paper outlines some key issues relating to religious diversity in the twenty-first century and how the movement of peoples worldwide contributes to those issues.