The submerged membrane bioreactor (SMBR) is a promising technology for wastewater treatment and water reclamation. This paper provides an overview of wastewater treatment in a submerged membrane bioreactor process with a special focus on municipal wastewater systems. SMBRs predict more than 95% organic removal with relative short hydraulic retention times (HRTs) of 1-8 h and NH(3) removal of more than 90% in the municipal wastewater treatment. It achieves 30% more removal of organic matter than activated sludge process. The COD can be reduced by 95%. Nitrification was complete and up to 82% of the total nitrogen could be denitrified. Nitrification/denitrification is sensitive to the feed quality, such as dissolved oxygen (DO) concentration, temperature, organic loads, inorganic/organic compounds and pH. The feed water composition, membrane geometry/configuration, membrane materials, and hydrodynamic effects are responsible for membrane fouling. These drawbacks can be reduced by maintaining turbulent conditions, operating at critical flux, and by selection of a suitable fouling resistance membrane material. Membrane washing is performed when the permeability is less than 10% of initial permeability. The reactor performance and the stability of the process and the membrane capacity are also discussed. Details of the various methods for washing are also included.