This document discusses frontiers and provides classifications of different types of frontiers. It defines a frontier as a politico-geographical area at the margin of a political unit's territory where expansion can occur. Frontiers are classified based on their relationship to a state's sovereignty, indigenous populations, pace of expansion, and degree of trans-frontier contact. Examples include political frontiers which mark the limits of de facto state control, and settlement frontiers which indicate stages of state expansion into new lands. Frontiers can involve inclusion or exclusion of indigenous groups and can be dynamic with continuous expansion or static if expansion is halted. The document also distinguishes between frontiers and boundaries, noting that frontiers are outward-oriented zones while boundaries are