Biogas production is growing nowadays due to the increasing installation of anaerobic digesters for organic waste treatment, mainly in Europe, promoted by the current environmental legislation. Depending on the final use, different biogas treatment steps are necessary since the biogas is mainly composed of methane, but also carries carbon dioxide and other minority substances such us hydrogen sulphide, oxygen, nitrogen, water, ammonia, siloxanes and particulates. In the last years, there is also an increasing demand for methane-rich biogas (biomethane) since the use of this product as vehicle fuel or its injection to the natural gas grid are becoming common practices. This supposes the biogas has to be first cleaned to remove the trace elements and then upgraded to remove CO2 and adjust the calorific value to the foreseen uses. Biogas upgrading is thus a key issue today to enrich biomethane to produce a natural gas substitute. This paper evaluates not only the biogas upgrading technologies that are commercially available today (as pressure swing adsorption, scrubbing using different types of absorbers, and gas permeation membranes), but also those that are under development trying to achieve lower investment and operational costs and, at the same time, higher methane content in the upgraded biogas (as membrane contactors, cryogenic upgrading, ecological lungs or in situ methane enrichment). They differ in functioning, the quality requirements for the incoming gas, the efficiency and their operational bottlenecks. Process technology, binomial energy-economy and environmental impacts will also be aspects to take into consideration in this paper. The review clearly suggests that water scrubbing technology, following by pressure swing adsorption methods are the most common, well established and conventional upgrading methods. On the other hand, membrane technology, especially membrane contactors, offers progressive research potential.