Several emerging technologies for treatment or resource recovery from wastewater are based on the combination of membranes and biochemical conversions. In this chapter, we review gas-diffusion, extractive, biocatalytic, and electrochemical membrane bioreactors (MBRs). Gas diffusion MBRs facilitate efficient delivery of a gaseous oxidant or reductant such as oxygen, hydrogen, or methane to microbial biofilms treating wastewater. Extractive MBRs completely separate the wastewater stream from the microbes and make toxic wastewaters amenable to biological treatment. Biocatalytic MBRs utilize enzymes or immobilized microbial cells for degradation of persistent xenobiotics or for synthesis of fine chemicals. Electrochemical MBRs make it possible to utilize organic in wastewater for production of energy or chemicals. All four technologies are currently in the research and development stage, but can potentially contribute to more efficient removal of pollutants and recovery of resources from wastewater.