Religion is a system of beliefs and practices that unite people in a moral community. Many religions include devotional practices, such as prayer and meditation, and a set of ethical guidelines for everyday life. Some religions have established educational and medical institutions and other social welfare networks. Whether or not you believe in God, religions have formed a large part of human history and culture, and continue to influence the lives of billions of people around the globe.

Most religions have some core elements in common, such as the tradition and maintenance of the belief system, sacred rites and rituals, a concept of salvation (either literal, with a heaven after death as in Christianity, or more symbolic, such as nirvana in Buddhism), sacred texts, a priesthood to lead the community, and places, objects, and days that are considered holy to believers. Some religions also have leaders or founders who gain godlike status and a central authority to which the followers look for guidance.

Anthropologists and sociologists who study the formation of human societies and cultures have different theories about why religion develops in the first place. Some researchers think that early humans created religion in response to a biological or a cultural need. The emergence of human consciousness, they argue, led to religion as a way to deal with questions about the meaning of life and death and the existence of uncontrollable forces in nature that could threaten their survival.

Other researchers, such as the psychologist Emile Durkheim, took a more functional approach to religion, defining it in terms of what binds a group of people together into a moral community regardless of whether or not they believe in any unusual realities. This approach to the concept of religion was a major contribution to the growth of comparative religious studies in the latter part of the 19th century.

Even so, the idea of what constitutes a religion continues to be fuzzy and the definition of religion has shifted over time. The term originally meant scrupulous devotion to a particular cause, but the term now encompasses many different types of spiritual beliefs and practices. As a result, the notion of what is and is not a religion tends to shift with changing intellectual fashions.