Across the world, most people are religious or spiritual, and many have a strong relational-emotional bond (attachment relationship) with God(s). This Element summarizes social-scientific theory and research on these relationships. Part I outlines basic principles of attachment and religion/spirituality. Part II describes normative (human-universal) processes and patterns. It explains how God and other supernatural beings often serve as irreplaceable relational caregivers (attachment figures), safe havens, and secure bases for people. Then it examines how religious/spiritual development interacts with attachment maturation across the lifespan. Part III explores individual differences in human and religious/spiritual attachment. After describing human-attachment differences, it examines how such differences can manifest jointly in forms of emotionally/socially correspondent or emotionally compensatory human attachment and religion/spirituality. Part IV discusses applied theory and research on religious/spiritual attachment. It explores the relationship between religious/spiritual attachment and health/well-being and concludes discussing how transformation in religious/spiritual attachment can occur through psychospiritual intervention or healthy relationships.