Molecular jets are seen coming from the youngest protostars in the early phase of low-mass star formation. They are detected in CO, SiO, and SO at (sub)millimeter wavelengths down to the innermost regions, where their associated protostars and accretion disks are deeply embedded and where they are launched and collimated. They are not only the fossil records of accretion history of the protostars but also are expected to play an important role in facilitating the accretion process. Studying their physical properties (e.g., mass-loss rate, velocity, rotation, radius, wiggle, molecular content, shock formation, periodical variation, magnetic field, etc) allows us to probe not only the jet launching and collimation, but also the disk accretion and evolution, and potentially binary formation and planetary formation in the disks. Here I review recent exciting results obtained with high-spatial and high-velocity resolution observations of molecular jets in comparison to those obtained in the optical jets in the later phase of star formation. Future observations of molecular jets with a large sample at high spatial and velocity resolution with ALMA are expected to lead to a breakthrough in our understanding of jets from young stars.
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