Multiple religious belonging, also known as double belonging, refers to the idea that individuals can belong to more than one religious tradition. While this is often seen as a common reality in regions such as Asia with its many non-exclusionary religions (such as Hinduism, Buddhism, Taoism, and Confucianism), religious scholars have begun to discuss multiple religion belonging with respect to religious traditions such as Judaism, Christianity, and Islam.

Those who practice double belonging claim to be an adherent of two different religions at the same time or incorporate the practices of another religion into their own faith life. It is increasing with globalisation. One such example is a person attending a Christian church but also finding meaning in yoga and in forms of meditation inspired by Eastern traditions, and enjoying attending a Jewish Seder at Passover.

The phenomenon of double belonging can occur within the same religion, where people hold membership in more than one Christian denomination, for example a Christian who is a church member of both the Catholic Church and the Religious Society of Friends. In the United States, nearly half of practicing Christians (46%) attend more than one church. The participation of Christians in church services of another denomination is seen as an expression of Christian ecumenism. In Christian monasticism, certain monasteries of one denomination accept oblates of the various Christian denominations that exist; for example, The Congregation of the Servants of Christ at St. Augustine’s House in Michigan, a Lutheran monastery, accepts Christian oblates who are Lutheran, as well as non-Lutheran. Certain church buildings are shared by two Christian denominations, such as the Cathedral of St Peter in Bautzen, which is shared by the Lutheran Church and the Catholic Church; both Lutherans and Catholics there will often worship together on occasions such as the New Year's Eve watchnight Mass.

In some religions, such as Judaism, Christianity, and Islam, those who hold an exclusivist understanding of religion see multiple religious affiliations as problematic. This is in contrast with religious persons in countries such as China, Japan, Korea, Vietnam, India, Nepal, and Sri Lanka, whose cultures have a long history of being influenced by different religions. Moreover, in the postmodernity, people tend to question their identity because of the unlimited choices of religions, which makes it difficult to define their identity.

Van Bragt showed that 79% of Japanese self-identify as Shintoists and 75% self-identify as Buddhists. The reason for the extremely high percentage of both religions is that many Japanese consider themselves to be both Shintoists and Buddhists and do not consider it a problem to belong to more than one religion. (Whether this statistic is correct is arguable.) This phenomenon, according to Van Bragt, is a "division of labour". Van Bragt argued that the cause of this phenomenon is that, different from the Western concept of religion, Shinto and Buddhism in Japan are defined by their rituals and practices, not by their moral and social authority. Thus, the Japanese can belong to several religions that do not conflict with each other in terms of social and ethical issues.

Scholars such as Catherine Cornille, Peter C. Phan, Francis Xavier Clooney, Jan Van Bragt, Aloysius Pieris, and Devaka Premawardhana have questioned the possibility of defining oneself as belonging to multiple religions. For these scholars, "religious belonging" is not an individual's subjective sense of a particular religion but rather, in Cornille's words, "the recognition of one's religious identity by the tradition itself and the disposition to submit to the conditions for membership as delineated by that tradition." For Cornille, the ultimate purpose of a scholarly discussion on multiple religious belonging is to transform one's religion through the understanding of other religions.

Based on Van Bragt's study, scholars have investigated the possibility that adherents of a religion such as Christianity may belong to multiple religions. The approach to Christian multiple religious belonging, according to Devaka Premawardhana, can be divided into two trends: Peter C. Phan's approach based on Christological grounds, in which he emphasises on Jesus's "asymmetrically superior status", and Francis Xavier Clooney's approach rooted in a methodological ground, which tries to cross boundaries into another religion just as religions must have discrete entities.^{[further explanation needed]} These two approaches are summarised below.

Phan's approach emphasised the assymmetricality in which Jesus is the Logos made flesh and the climax of God dealing with humankind. In an attempt to resonate with one's cultural identity and tradition, Phan explained that multiple religious belonging is necessary for practitioners of multiple belonging to treat other religions as a qualifier of their identity. This approach, according to Phan, does not deny one's Christian identity, which functions substantively alongside non-Christian religions. Phan noted that multiple religious belonging is not a new issue in the twenty-first century but rather the common form of life of the first-century Christians—whom at the time were predominantly Jewish Christians—recorded in the book of Acts. In Phan's view, the disappearance of this trend was "a tragic loss to both Judaism and Christianity", because it led to a subsequent history of bitter hatred, especially from the side of Christianity.