Extrusion is a widely used process in the industry to produce foods with specific technological properties (color, texture, aroma, etc.). Its use dates back to the 1950s, mainly in extrusion cooking. Extrusion cooking is considered as a thermoplastic process, whose treatment is done at high temperature and with a short residence time. The mechanical action combined with the high temperature allows the modification of the internal structure of the matrix introduced and therefore its properties. Two types of extruders can be used, with different performance and capabilities, single-screw extruders, and twin-screw extruders. The mechanical treatment of the extruders can be carried out directly in the dry process, or by addition of solvents, and in this context, it is the twin-screw extrusion that is preferred. The twin-screw extruder is a tool that allows to work continuously in many different conditions, which has favored its use in very different fields such as the paper or the chemical industry. It is an instrument increasingly studied in the context of the biorefinery, since it allows the treatment of both green plants, such as alfalfa, and dry residues such as cakes or straw.