Anaerobic membrane reactors (AnMBRs) have recently evolved from aerobic MBRs, with the membrane either external or submerged within the reactor, and can achieve high COD removals (similar to 98%) at hydraulic retention times (HRTs) as low as 3 h. Since membranes stop biomass being washed out, they can enhance performance with inhibitory substrates, at psychrophilic/thermophilic temperatures, and enable nitrogen removal via Anammox. Fouling is important, but addition of activated carbon or resins/precipitants can remove soluble microbial products (SMPs)/colloids and enhance flux. Due to their low energy use and solids production, and solids free effluent, they can enhance nutrient and water recycling. Nevertheless, more work is needed to: compare fouling between aerobic and anaerobic systems; determine how reactor operation influences fouling; evaluate the effect of different additives on membrane fouling; determine whether nitrogen removal can be incorporated into AnMBRs: recover methane solubility from low temperatures effluents; and, establish sound mass and energy balances. (C) 2012 Elsevier Ltd. All rights reserved.