Ductility plays an important role in structural and seismic engineering. Its beneficial effect on load distribution and performance during earthquakes is assumed to be true also for anchors connecting concrete and steel elements. However, a conclusive definition of ductility for post-installed concrete anchors is not given yet in the relevant qualification guidelines and design codes. The goal of this paper is to define anchor ductility based on the load-displacement behavior of installed anchors, and to evaluate available displacement capacities and their impact on seismic anchor design. The background of anchor ductility was investigated and meaningful anchor ductility parameters were developed based on the database of several hundred tests on diverse anchor types. Finally, the effects of anchor displacements on the behavior of structural and nonstructural connections during earthquakes are discussed.