Membrane systems have become a tried and accepted gas treating technology. Membrane technologies are easily applicable to biogas upgrading and offshore and onshore natural gas treating facilities to remove CO2. Biogas is produced during the anaerobic digestion of organic substrates, such as manure, the organic fractions of household and industry waste, sewage sludge, and energy crops. It mainly consists of methane (55–65% vol) and CO2 (35–45% vol) depending on the substrate, together with impurities such as siloxanes, halides, H2S, NH3, and volatile organic compounds (VOCs), and can be utilised without significant treatment as a renewable energy in combined heat and power generators or, after upgrading (boosting of its calorific value by increasing the methane concentration), as a substitute of natural gas from wells. Membrane technology can play a key role in the purification and upgrading of biogas and, in this chapter, the first large commercial scale upgrading plant installed in Italy for the treatment of 6250 Nm3 h−1 biogas is described.