It is shown how stability theory of dynamic systems, emerging from various beginnings strewn over the realm of mechanics, developed into a unified, comprehensive theory for dynamic systems with a finite number of degrees of freedom. It is then demonstrated, how such theory could be adapted over the last five decades to the specific nature of stability problems involving continuous elastic systems. The need for such adaption is stressed by pointing to systems with follower forces. The difficulties arising from the fact that continuous systems are systems with an infinite number of degrees of freedom are emphasized, and an adequate approach to a unified stability theory including also continuous systems is outlined.