People construct and use boundaries to sort and manage unordered experience. Boundaries thus become active mechanisms for creating and maintaining experiences of self. Under optimal circumstances, boundaries function as transitional realms that paradoxically join and separate areas of experience. Such paradoxical functioning allows individuals to simultaneously maintain a distinct sense of self yet remain open to new possibilities. By identifying and describing variations in boundary functioning, the author provides a process-oriented mechanism for understanding clinical presentations. Developmental aspects of boundary formation and maintenance are also explored. Over time, habitual preferences for managing awareness comprise persistent boundary patterns—both within internal awareness and between individuals or groups.