Models of molecular outflows

In this contribution, I present a broad historical review of the various hydrodynamical models that have been considered for explaining molecular outflows, and of their merits and failures when compared with observations. Wind-driven bubbles, viscous jet mixing-layers, and jet bowshocks, are discussed in turn. Most general properties of outflows can be understood in terms of a simple bowshock model. However, the detailed structure of outflows is more complex and not yet fully understood, given the presence of time variability in the jet velocity and/or direction. Finally, I discuss constraints on wind properties (momentum, mass-loss rate, radius) that can be derived from molecular outflows driven by jet bowshocks.