 The failure to find the features of classical chaos in quantum systems is usually diagnosed as being due to the linear nature of Schrödinger’s equation (classical chaos appears to require nonlinearity as a necessary condition). And the evidence from isolated quantum systems substantiates this diagnosis as just discussed. What about interacting quantum systems (which sometimes get called open quantum systems)? At first glance, one can argue that the linearity of Schrödinger’s equation implies that nearby quantum states will always remain nearby as they evolve in time. However, some alternative possibilities for possible chaotic behavior have been proposed for interacting quantum systems. 