An investigation into the aeroelastic characteristics of a wind tunnel model all-movable vertical tail with variable attachment position and stiffness has been made. An initial analytical study investigated the effect of varying the torsional stiffness and position of the single root attachment. An attachment was designed and manufactured that enabled an existing wind tunnel model to behave as an all-moving fin in order to validate the analytical results. This initial study showed that in order to get the full benefits of such a design, whilst still meeting aeroelastic constraints, the torsional stiffness must be adaptive so that it can be adjusted at different regions of the flight envelope. A further variable stiffness attachment was then designed and manufactured that enabled fully adaptive torsional stiffness control. Bench-top tests were performed to validate the structural behaviour of the models, followed by wind tunnel tests to examine the aeroelastic characteristics of the vertical tail models, in particular the aeroelastic effectiveness. The experimental results compared well with theoretical predictions. It was shown that it is possible to control the torsional stiffness, and hence the aeroelastic characteristics, of the all-moving vertical tail using the adaptive stiffness devi ce.