Transformations of biomass into fuel components and chemicals have attracted enormous attention in the recent years. Owing to the complexity and diversity of these feedstocks, new applications and conversion process have to be sought. In the chapter we focus on the use of heterogenous catalysis, in particular molecular sieves, for adding value to biomass-drived feedstocks. Special emphasis is put on the discussion of the selected transformations in the view of the characteristic properties of molecular sieves. After analysing the available types of biomass feedstocks according to their complexity, the next part is devoted to reviewing of the current developments in the conversion of lignocellulosic biomass, triglycerides, glycerol, sugars and sugar alcohols, aldehydes and ketones from biomass pyrolysis, and terpenes. Finally, the different types of molecular sieves and their basic properties and application possibilities are discussed with regard to the specific needs of biomass transformations