A variety of philosophical, religious, spiritual, and scientific perspectives converge on the notion that everything that exists is part of some fundamental entity, substance, or process. People differ in the degree to which they believe that everything is one, but we know little about the psychological or social implications of holding this belief. In two studies, believing in oneness was associated with having an identity that includes distal people and the natural world, feeling connected to humanity and nature, and having values that focus on other people’s welfare. However, the belief was not associated with a lower focus on oneself or one’s concerns. Participants who believed in oneness tended to view themselves as spiritual but not necessarily religious, and reported experiences in which they directly perceived everything as one. The belief in oneness is a meaningful existential belief that has numerous implications for people’s self-views, experiences, values, relationships, and behavior.