Abstract: The attached paper is a draft of the concluding chapter in a book about religion in relation to other social systems (governments, economic markets, and secular social groups and entities). Prior chapters reviewed multiple theories and many empirical studies, as well as social-science scholarship, bearing on the relative advantages and costs of the four types of systems as they attempt to provide multiple kinds of benefits for human individuals and groups. The attached table of contents may give a more concrete sense of those inquires. A general theme that emerged was that the four systems not only have relative advantages and disadvantages that vary by type of benefit or cost, but also by specific context and over time, as there are changes in external factors like social scale and technological developments. Some general trends are identified in the prior chapters. The final chapter is deliberately cast as a reflective essay. It speculates about the future of religion over the next several centuries (e.g., to the year 2500), and identifies three categories of predictions: virtually complete decline; fluctuating endurance; and morphological evolution. It then considers high-level arguments for and against them. For example: (1) The virtually complete secularization model seems supported by trends in some advanced economies, e.g., in western Europe and more recently in the US, by reflection on efficiency improvements in the other social systems, and by arguments about the impact of science and reason on religious beliefs. But the better and more comprehensive global demographic evidence indicates a very different pattern of trends. The essay reflects on likely explanations of the conflict between prediction and evidence, ranging from the differential fertility rates of secular and religious groups to theological moves in all dominant world religions that aim to blunt the apparent conflict between reason and religion. (2) The fluctuating endurance model is supported by some painstaking historical accounts of the development of religions over the centuries. But it is also called into question by historical studies of the evolution of religions over the millennia, and by recent multidisciplinary work on cultural evolution. (3) The same historical and multidisciplinary work also supports the plausibility of expecting another fairly fundamental evolution in the features of those world religions, or spinoffs from them, that will be successful in the future. To explore this possibility more systematically, the paper first offers ideal-type general descriptions of three prior stages – religion for good personal fortune; religion for public goods; and religion for pro-social norms – and offers thoughts on how the later stages each involved changes along multiple but related dimensions of religion and how those changes were related to changes in the typical external human environment. Finally, the paper then speculates about a plausibly emerging fourth stage – religion for expanding circles – in which there is more emphatic, widespread, and effective emphasis on norms relating to moral concern for out-groups and future generations, and ties such shifts to mega-changes (like greater globalization and environmental sustainability challenges) in the modern human environment. It then imagines, as a thought experiment, how the seven typical mechanisms of the dominant world religions might be modified in the fourth stage.