A composite polyamide filtration membrane is disclosed. The membrane comprises a porous support, a polyamide layer on the porous support, optionally a polyhydroxy layer on the polyamide layer, and an anti-fouling coating grafted on to the polyamide layer or the polyhydroxy layer (if present). The anti- fouling coating comprises a zwitterionic polymer. A process for producing a filtration membrane having an anti-fouling coating is also disclosed.