Star formation proceeds from the gravitational collapse of molecular clouds. A characteristic phenomenon associated with this phase is the ubiquitous presence of molecular outflows originating from the central protostar. These outflows probably help the stars to dissipate their angular momentum, but the details of the mechanism are not fully understood. Left : Interferometer map of the molecular jet in the HH211 outflow; the CO emission (white lines) is overlaid on a false color image of excited molecular hydrogen. The red lines delineate a flattened dust concentration around the protostar.