More than 1800 brown seaweed species that come under Phaeophyta are known to have importance in the seaweed industry as well as from an ecological point of view. Traditionally, brown seaweed biomass was used for a long time to produce alginate. However, in the past few years, it has gained recognition as an important raw material to produce several other products, such as plant biostimulants, minerals, PUFAs, cellulose, and proteins. This chapter presents a brief account of brown seaweeds, starting with their introduction, composition, extraction process, products, and applications. The biorefinery approaches developed for the sustainable utilization of brown seaweed biomass were also discussed in detail.