This paper gives a brief introduction and review of linear stability theory
with emphasis on nonmodal effects. The temporal and spatial framework is d
iscussed and the response to periodic and stochastic forcing is addressed.
An extension to nonautonomous evolution problems is presented. Bypass trans
ition due to the secondary instability of streaks is used as an example to
illustrate the role of a nonmodal linear mechanism in the breakdown to turb
ulence. (C) 2000 American Institute of Physics. [S1070-664X(00)97105-2].