  We review the known properties of molecular outflows from low- and high-mass
young stars. General trends among outflows are identified, and the most recent
studies on the morphology, kinematics, energetics, and evolution of molecular
outflows are discussed, focusing on results from high-resolution millimeter
observations. We review the existing four broad classes of outflow models and
compare numerical simulations with the observational data. A single class of
models cannot explain the range of morphological and kinematic properties that
are observed, and we propose a possible solution. The impact of outflows on
their cloud is examined, and we review how outflows can disrupt their
surrounding environment, through the clearing of gas and the injection of
momentum and energy onto the gas at distances from their powering sources from
about 0.01 to a few pc. We also discuss the effects of shock-induced chemical
processes on the ambient medium, and how these processes may act as a chemical
clock to date outflows. Lastly, future outflow research with existing and
planned millimeter and submillimeter instruments is presented.
