Religion consists of cultural and psychological aspects of human life, including beliefs, behavior, values, morals, and devotional practices that impact the worldviews and lifestyles of believers. It may involve a belief in spirits or supernatural entities and an emphasis on moral conduct, the afterlife, worship, prayer, and rituals. Religion also includes a moral code and a set of writings, traditions, or beliefs that are revered as sacred. It is often a focus of social institutions, such as churches and synagogues, and individuals participate in religious activities ranging from worship to prayer to community service.

The concept of religion has evolved from tribal totems and ancestor worship to a wide range of philosophies and practices. Despite this diversity, religions have some common features that make them worthy of the name and a classification as a form of human activity. The first historical religions, for which we have a record, are thought to have emerged along the Nile River in Egypt and in Mesopotamia around 5,000 years ago. These early religions were polytheistic, meaning they recognized multiple gods.

Scholars have debated the nature of religion over the centuries, with many arguing that it is a social construct. As such, it is not a real thing that exists in all cultures or communities. Other scholars, particularly those influenced by the works of Michel Foucault and Friedrich Nietzsche, have drawn attention to the power dynamics that underlie the construction of concepts like religion. They have urged that before we study the phenomenon, we must understand how it is constructed.

In recent decades, there has been a move toward a more reflexive approach to the study of religion, as some scholars have pulled back the camera, so to speak, and looked at how our definitions affect our conclusions (see Greil and Rudy 1990 on “quasi-religions”). This has led to a recognition that it is possible to construct different theories about the same phenomena based on different definitions of what constitutes religion. This awareness has brought to the forefront questions of whether it is useful or even possible to define religion (see Southwold 1978).

There are a variety of different approaches to defining religion, which are classified as either substantive or functional. A realist, such as Karl Marx, would argue that there is no such thing as a religion, while a functionalist, such as Emil Durkheim, would say that one can define it by its function in the life of a culture, or even a person.

The realist position, which has been criticized by those who see it as too narrow in its focus on belief and experience, can also be critiqued for being ethnocentric. By focusing on Western religion and treating the dichotomy between natural and supernatural as essential, it excludes faith traditions that emphasize immanence or oneness, such as some forms of Buddhism and Jainism. By contrast, a functional approach, which can be critiqued for its lack of objectivity, can still provide useful and interesting results.