This chapter explores the complex realm of β-glucan (BG), a polysaccharide that is well known for its variety of sources and significant health advantages. BG, which is mostly made up of glycosidic linkages connecting D-glucose polymers, is an essential part of dietary fibre and can be found in a variety of foods and environments, including cereal grains, edible mushrooms, bacteria, yeast, and fungus. Oats and barley are notable cereals that are rich in β-glucan, falling under the category of non-starch polysaccharides. The unique structural complexity of different sources of BG affects their solubility, digestibility, and physiological effects. β-glucan is present in cereal grains as fibrous structures, primarily with β-(1 → 3) and β-(1 → 4) connections. On the other hand, non-cereal sources such as bacteria, algae, yeast, and mushrooms feature varied linkages, influencing the quality of BG and its chemical attributes.