The theories for the free fligbt motion of miseiles, as generally considered by the aerodynamicist and the ballistician, are combined to yield a single theory for the basically symmetrical missile. The force and moment system contains not only the usual aerodynamic forces and moments but also the effects of slight configurational asymmetries and the effects of rolling velocity. The theory yields the condition for the dynamic stability of both statically stable and statically unstable missiles, and alco predicts that the presence of configurational asynnetries together with rolling velocity may result in resonance instability. Numerical integrations of the differential equations for the pitching and yawing motion are carried cut for three variations in the rolling motion. The results indicate that the rapidity of passage through the resonance region is a significant factor affecting the nagnitude of the pitch and yaw of the missile. rWo models of a simple arrow type missile having control surface deflection are gun launched at supersonic velocity in the Aberdeen Spark Photography Range and the free flight pitching and yawing motion and the transverse displacement are measured. The tricyclic theory is fitted to the experimental data. The results indicate tbat the theory accurately represent. the actual motion of the two models and that the associated static and dynamic aerodyamic derivatives are accurately determined.