This paper explores the multifaceted nature of β-glucan, a notable dietary fiber (DF) with extensive applications. Beginning with an in-depth examination of its intricate polysaccharide structure, the discussion extends to diverse sources like oats, barley, mushrooms, and yeast, emphasizing their unique compositions. The absorption and metabolism of β-glucan in the human body are scrutinized, emphasizing its potential health benefits. Extraction and purification processes for high-quality β-glucan in food, pharmaceuticals, and cosmetics are outlined. The paper underscores β-glucan’s biofunctional roles in immune modulation, cholesterol regulation, and gastrointestinal health, supported by clinical studies. The review discusses global trade dynamics by tracing its evolution from a niche ingredient to a global commodity. In summary, it offers a comprehensive scientific perspective on β-glucan, serving as a valuable resource for researchers, professionals, and industries exploring its potential in the dietary fiber landscape.