  We study the stability of periodic trajectories of planar inverse magnetic
billiards, a dynamical system whose trajectories are straight lines inside a
connected planar domain $\Omega$ and circular arcs outside $\Omega$. Explicit
examples are calculated in circles, ellipses, and the one parameter family of
curves $x^{2k}+y^{2k}=1$. Comparisons are made to the linear stability of
periodic billiard and magnetic billiard trajectories.
