For a hundred years or more, oil and natural gas has supplied fuel and other raw chemicals to support economic growth. In the last decades their shrinking reservoirs and the increasing cost of production has become obvious, leading researchers to look for alternative substitutes of all the chemical materials presently derived from oil and gas. This review is focused on xylan, the second most abundant plant polysaccharide on our planet. Some xylan-derived products have already found commercial applications (ethanol, xylitol, xylo-oligosaccharides) while others could have a great future in a wide range of industries. The chemical and structural variations of xylans produced by different plants, and the concentration of xylan in various plant resources are summarized. This review discusses the latest research developments in extraction and purification methodologies, and chemical modification, as well as the analytical methods necessary for xylan related research.