This review focuses on the role of sensori-motor function in the healthy as well as the functionally unstable ankle. The concept functional ankle instability--a widely used term, which has no universally agreed upon definition-as well as the sources of peripheral afferent information measured with different sensori-motor tests are discussed. The protective mechanisms against sudden ankle inversion are reviewed, and models that directly connect deficits in kinaesthesia and peroneal reflex reaction to an increased risk of sustaining unprovoked ankle inversion injuries are presented.