I discuss in this contribution constraints on the origin of mass-lossfrom young stars brought by recent observations at high angularresolution (0.1'' = 14 AU) of the inner regions ofwinds from T Tauri stars. Jet widths and collimation scales, the largeextent of the velocity profile as well as the detection of rotationsignatures agree with predictions from magneto-centrifugal disk windejection models. However dynamically cold disk wind solutions predicttoo large terminal velocities and too low jet densities and ionisationfractions, suggesting that thermal gradients (originating in anaccretion heated disk corona for example) may play an importantrole in accelerating the flow.