Copious research exists regarding ankle instability, yet lateral ankle sprains (LAS) persist among the most common recurrent musculoskeletal injuries. Key anatomical structures, necessary to subtalar joint (STJ) stability, have been potentially overlooked. The functional STJ complex is comprised of 2 compartments – the talocalcaneal joint (posteriorly) and the talocalcaneonavicular joint (anteriorly). Stability is provided by extrinsic ligaments (calcaneofibular and deltoid ligaments) and a series of broad intrinsic ligaments situated in the tarsal canal. These intrinsic ligaments, separating the 2 compartments, are a crucial source of mechanical stability and proprioceptive information. The specific stabilising direction of the STJ complex is controversial; there is likely a multiplanar function, similar to the ACL. Damage to the STJ complex occurs in approximately 25%–80% all LAS injuries, especially when the lateral ligaments are also involved. STJ complex disruption allows non-physiologic anterolateral rotary displacement, especially in weight-bearing. Patients with STJ instability present similarly to those with chronic ankle instability (CAI), including a history of acute LAS, recurrent ‘giving way’ episodes, insecurity on unstable surfaces, recurrent swelling, stiffness, and diffuse hindfoot pain that is aggravated by activity or uneven ground. Persistent pain over the sinus tarsi is common. Few special tests for STJ instability exist. Imaging with stress radiograph, diagnostic ultrasound, and MRI all have varying degrees of effectiveness of visualising soft tissue damage within the STJ complex. Laboratory-oriented evidence supports the vital role of ankle intrinsic ligaments for ankle instability, yet clinically-relevant research on evaluating and treating the STJ complex lags. This critical review summarises the literature, providing model to support further investigations into the role of the STJ complex in CAI. Future research should focus on identifying the clinical population overlap of CAI patients and those with concurrent STJ complex instability, and the best practices for clinical action when the intrinsic ankle ligaments are involved.