We now believe that the birth of all stars is accompanied by fast and energetic mass loss in the form of bipolar winds and jets. This violent phase of protostellar evolution has a strong impact both on the evolution of the protostar itself and the surrounding molecular cloud. This talk will review current observations of these objects, including observations at radio, millimetre, infrared and optical wavelengths, and the models which have been used to explain their observed structure. In particular, the idea that the molecular flows are driven by high-Mach-number atomic jets will be critically evaluated, and the properties of the driving jets will be presented. The evolution of outflows and its relationship to the evolution of the central protostellar system will also be discussed.