In this chapter, some building-block chemicals that play important roles in an industrial application are summarized. These building blocks are usually referred as bio-based chemicals that are produced by biological routes using substrates as pure sugars or even renewable biomass including cellulosic and lignocellulosic materials. C3 (glycerol and 3-hydroxy propionic acid), C4 (succinic acid, malic acid, itaconic acid, glucaric acid, glutamic acid, and l-aspartic acid), C5 (xylitol and levulinic acid), and C6 (sorbitol) bio-based chemicals have been selected for discussion due to their capability to be utilized in broad applications and to replace existing petroleum-based chemicals in commercialized scales in high volume. Biological techniques including metabolic engineering either by an inactivation or overexpression of interested genes or both, metabolic evolution, and enzymatic catalysis that are related to construct efficient microbial strains and even to optimize parameters affecting suitable fermentation conditions for developed microorganisms are employed for sustainable productions of these bio-based chemicals. © 2022 Elsevier Inc. All rights reserved.