Abstract: Continuous permeable graphene films having 2 or more layers of graphene and wherein nanochannels or nanopores extend through said film. Each nanochannel is comprised of a fluidly connected series of gaps between edge mismatches of adjacent graphene grains within said 2 or more layer adjacent sheets, said nanochannels providing a fluid passage from one face of the permeable graphene film to the other. Also, membranes including a permeable support membrane overlaid by a continuous permeable graphene film and processes for the preparation of said membranes. Also the use of said membranes in water purification and desalination, for example.