Abstract: Forward osmosis membrane vessels, and particularly stackable forward osmosis membrane vessels, are provided as well as systems and methods thereof. The forward osmosis membrane vessel has a body, a strong draw solution chamber, a first and a second semipermeable membrane, and a brine chamber. The first and second semipermeable membranes each are disposed within the cavity of the body. The first and second semipermeable membranes are configured to produce diluted draw solution streams and brine streams. The brine chamber is disposed at least partially between the first semipermeable membrane and the second semipermeable membrane. The forward osmosis membrane vessel may be configured such that in a stacked configuration the brine chamber and the strong draw solution chamber of the forward osmosis membrane vessel aligns with a brine chamber and a strong draw solution chamber of an adjacent second forward osmosis membrane vessel.