The present study reviews the most recent research published (starting approximately in the 1980s) on the composition of plant cell walls, with a description of the polysaccharides contained in the microfibrillar and amorphous phases: cellulose, hemicellulose and pectic substances, as well as the other components: lignin, proteins and enzymes. Cellulose is a linear homopolymer made up of microfibrils that form a para-crystalline structure stabilised by hydrogen bridges. The hemicelluloses constitute an important group of polysaccharides, which are inter-linked and also linked to microfibrils of cellulose and/or pectins, the most important being: xylans, arabinoxylans, mannans, galactomannans, glucomannans, arabinogalactan II, beta-1,3-glucan and beta-1,3-beta-1,4-glucans. The pectic substances are a complex mixture of colloidal polysaccharides that can be extracted from the cell wall with water or chelating agents, the most significant being: rhamnogalacturonan I, rhamnogalacturonan II, arabinan, galactan, arabinogalactan I and D-galacturonan.