Plant biomass always consists of the basic precursor: carbohydrates, lignin, proteins and fats, beside various substances such as vitamins, dyes, flavours, and aromatic essences. Biorefineries combine the essential technologies between biological raw materials and the industrial intermediates and final products. In this chapter, the lignocellulosic feedstock system, technologies and products are considered. In particular, focus is directed on the platform chemicals (building blocks) furfural, levulinic acid, hydroxymethylfurfural, sugar alcohols, and lactic acid obtained by thermochemical conversion methods, as well as synthesis gas. The article gives an overview over different production methods and several applications of these building blocks.