We propose a three-year study on an investigation of control based on instability of a developing trailing vortex. Trailing vortices have many adverse effects in both aeronautical and maritime applications, including increased drag, wake-hazard, vortex detection and noise. Our previous experimental research has shown that active circulation control of a trailing vortex, while potentially effective, has a large parameter space, making an experimental or computational parametric study unwieldy. To navigate and optimize the control parameters, an instability analysis on a developing trailing vortex is proposed. First, a parabolized stability analysis is performed on the slowly developing vortex just downstream of the airfoil trailing edge. Then, the adjoint parabolized stability equations can be solved to determine structure of the disturbance and the most unstable wavelengths and frequencies. With this knowledge, a physics-based active control system that leverages the observed instabilities along the wing surface is examined in wind tunnel experiments.