A study of rotor blade aeroelastic stability is carried out, using an analytic model of a two-dimensional airfoil undergoing dynamic stall and an elastomechanical representation including flapping, flapwise bending, and torsional degrees of freedom. Results for a hovering rotor demonstrate that the models are capable of reproducing both classical and stall flutter. The minimum rotor speed for the occurrence of stall flutter in hover is found to be determined from coupling between torsion and flapping. Instabilities analogous to both classical and stall flutter are found to occur in forward flight. However, the large stall-related torsional oscillations which commonly limit aircraft forward speed appear to be the response to rapid changes in aerodynamic moment which accompany stall and unstall, rather than the result of an aeroelastic instability.