'Symbolic Boundaries' are the lines that include and define some people, groups, and things while excluding others. These distinctions can be expressed through normative interdictions (taboos), cultural attitudes and practices, and patterns of likes and dislikes. They play an important role in the creation of inequality and the exercise of power. The term 'symbolic boundaries' also refers to the internal distinctions of classification systems and to temporal, spatial, and visual cognitive distinctions in particular. This article focuses on boundaries within and between groups. It discusses the history, current research, and future challenges of work on this topic.