Alginates are natural exopolysaccharides produced by seaweeds and bacteria belonging to the genera Pseudomonas and Azotobacter. Due to exhibiting unique physicochemical properties, they have been widely applied for various industrial purposes such as in food, agricultural, cosmetic, pharmaceutical, and biomedical industries. In the last two decades, they have found their way into the advanced pharmaceutical and biomedical applications, owing to their biocompatibility and non-toxicity as well as versatility in view of modifications. So far, algal alginates have been the sole commercialized products applied for various purposes, while the potential uses of bacterial alginates remain unharnessed. Importantly, algal and bacteria alginates differ substantially from each other with respect to their composition, modifications, molecular mass, viscoelastic properties, and polydispersity. Indeed, bacterial alginates may meet current needs in the field of advanced pharmaceutical and biomedical engineering. In this chapter, after a brief overview of alginate discovery, general properties, applications, and comparative assessment of algal and bacterial resources, current findings about the biosynthesis of alginates, mainly in bacteria, will be discussed. Furthermore, we will discuss the current understanding of alginate polymerizing and modifying enzymes and their structure-function relationship. Knowledge about alginate biosynthesis/modification enzymes provides foundation for rational design of cell factories for producing tailor-made alginates. As a conclusion, advanced understanding of alginate biosynthesis pathway and involved enzymes creates an opportunity for bioengineering and synthetic biology approaches toward the production of alginates exhibiting desired material properties suitable for pharmaceutical and biomedical applications.