Our understanding of social anxiety disorder (also known as social phobia) has moved from rudimentary awareness that it is not merely shyness to a much more sophisticated appreciation of its prevalence, its chronic and pernicious nature, and its neurobiological underpinnings. Social anxiety disorder is the most common anxiety disorder; it has an early age of onset--by age 11 years in about 50% and by age 20 years in about 80% of individuals--and it is a risk factor for subsequent depressive illness and substance abuse. Functional neuroimaging studies point to increased activity in amygdala and insula in patients with social anxiety disorder, and genetic studies are increasingly focusing on this and other (eg, personality trait neuroticism) core phenotypes to identify risk loci. A range of effective cognitive behavioural and pharmacological treatments for children and adults now exists; the challenges lie in optimum integration and dissemination of these treatments, and learning how to help the 30-40% of patients for whom treatment does not work.