From its first appearance on Earth 1.5 billion years ago, algae have been a major part of the carbon cycle and were also a source of food for many indigenous tribes around the world. Until recently, applications of algae were limited, and its tremendous potential is only now being explored. Being a rich source of homo- and hetero-polysaccharides, their bioactivity can be exploited to manufacture various value-added products. From producing biofuels to pharmaceuticals, and from agriculture to cosmetic industries, the range of applications of algal polysaccharides is extensive. Unique types of algae found in marine ecosystems are eminent source of algal polysaccharides as they constitute 15–75% of the cell dry weight. Microalgae magnify our path toward a sustainable future due to their intracellular, extracellular, and cell wall polysaccharides, which hold immense potential for various industrial applications. This chapter focuses on different types of algal polysaccharides, their biosynthesis, properties, production, extraction, and applications. Algal polysaccharides such as agar, alginates, carrageenan, and ulvans are well-studied polysaccharides that are largely applicable in food, pharmaceutical, biomedical, and agricultural industries. These polysaccharides are biocompatible, biodegradable, renewable as well as safe for human consumption. Despite the recent popularity, there is a disparity in our knowledge of algal polysaccharides, their structure, biosynthetic pathways, and various unexplored polysaccharide hydrolases (polysaccharide degrading enzymes). The physical and chemical properties of algae are responsible for these limitations. Many algae pose a naturally low yield of polysaccharides which can be increased by novel methods for production, extraction, and better infrastructure.