Accumulative evidence suggests that resident gamma delta T cells in epithelia are biologically distinct from systemic gamma delta T cells in the circulation. Murine resident gamma delta T cells have innate immune characteristics and play an important role in tissue homeostasis after damages. In contrast, a unique subset of circulating gamma delta T cells in primates, like alpha beta T cells, can mount adaptive immune responses in infections. This article compares biological features between resident and circulating gamma delta T cells.