The use of membranes for selective CO2 separation from biogas, also commonly known as biogas upgrading, is reviewed in this chapter. Nowadays, compared to other well-established technologies such as pressure swing adsorption (PSA), or scrubbing, membrane technology has not found large industrialization for biogas upgrading because of the current limitations of polymer-based materials. Despite these limitations, membrane technology has a great potential for selective CO2 separation because the separation mechanism is the simplest among all technologies. Furthermore, the costs of membrane fabrication and subsequent operation are rather low, thus making membrane technology an interesting alternative for upcoming biogas upgrading plants. The current efficiency of membrane technology in biogas upgrading systems is lower compared to conventional technologies, and therefore current research is focused on the development of improved membranes with higher selectivity and CO2 fluxes per membrane area. In this chapter, the state of the art of the membrane technology and the recent developments of novel membrane materials are given, and the future trends and economics of the technology summarized.