This project, for the first time in faith development research, aims at cross-culturally documenting religious development across time using a longitudinal design that includes large-scale re-interviewing with the faith development interview, triangulated with extensive questionnaire data. This project will be based on samples in Germany and the USA covering the adult life span and a wide variety of religious persuasions and world views, including non-theists. This project can capitalize on the data and experience accumulated in past Bielefeld-based research projects. We were continuously engaged in the re-specification of evaluation procedures: The 4th edition of the Manual for Faith Development Research is in press and will replace the 3rd edition. At the end of 2017, our data base will consist of ca. 900 FDIs in combination with questionnaire data that include, besides many other scales, the Religious Schema Scale, our quantitative instrument for religious styles development. Conceptually, the religious styles perspective, which has been developed in critical appreciation of James Fowler’s seminal work, will structure this project. This project continues the successful collaboration of H. Streib, R.W. Hood and their teams in cross-cultural and multi-method research on religious development in the Deconversion Project, the Spirituality Project, and the current study of Developmental Change in Spirituality, which is funded by the JTF for the USA and by the DFG for Germany. Research questions include: Can progressive religious development be corroborated? Is there also regression? Is the advancement of religious development associated with the emergence of a dialogical style? What are correlates and predictors for change? Outputs include, besides conference presentations and papers in high-ranking journals, two major volumes, and, importantly: the creation of a global network of experts and researchers in religious development.