Van der Waals heterostructures composed of stacked atomically thin layers can exhibit novel phenomena due to the unique layer-layer interactions. In this talk, I will describe our studies of ultrafast charge transfer between different transition metal dichalcoginide layers. This not only leads to ultrafast charge separation, but also enables the generation of high-purity and long-lived valley polarization with microsecond lifetime in WS2/WSe2 heterostructures. I will also discuss spatially and temporally resolved imaging of pure valley and spin current in the WS2/WSe2 heterostructure.