Functional components of food are the standardized and characterized fractions or extracts containing bioactive ingredients or non-conventional nutrients of varying purity. β-glucans are part of these functional components. They are naturally occurring constituents of the cell walls of cereals and certain bacteria and fungi where they exist as soluble dietary fibre. Chemically, they are non-starchy polysaccharides. Structurally, they are heterogeneous group of glucose polymers, consisting of a backbone of β(1,3)-linked D-glucopyranosyl units to which either β(1,6) or β(1,4) side chains of varying distributions and lengths are linked. Cereal and bacterial β-glucans are primarily linear with large regions of β(1,4) linkages separating shorter stretches of β(1,3) structures. Fungi β-glucans have short β(1,6)-linked branches coming off the β(1,3) backbone while those of yeast have β(1,6) branches that are further elaborated with additional β(1,3) regions. These structural differences do have large implications and impact on their activities. β-glucans have plenty of health benefits including the control of blood cholesterol, low glycaemic response, prebiotic, and immunomodulatory effects. In addition, the multidimensional and functional characteristics of β-glucans are of great commercial and nutritional importance with great potentials of application in the food and pharmaceutical industries as stabilizers, viscosity enhancers, fat substitutes, gelling and plasticizing agents. Based on supporting scientific evidences, various health claims in respect of β-glucans have been verified and approved in the U.S., U.K., Sweden ant the EU. This paper, therefore, reviews current developments on β-glucans as functional components of food with regards to their physiological benefits, health claims and applications.