Social anxiety disorder (SAD) was differentiated from other forms of anxiety disorders by researchers nearly 40 years ago. Social phobia is another terminology for SAD in the literature. Individual suffering with SAD feel fearful in social situations and more often than not avoid them just to evade anticipated scrutiny. Social anxiety disorder (SAD) usually starts at very young age, with generalize type appearing as early as childhood. However, both adults and adolescents had a similar prevalence of SAD (6–8%) in one of the studies. SAD is one of the most universal reasons for school refusal and dropouts, and it is not unusual to see the disorder take a chronic course. This chapter covers the epidemiology of SAD, diagnosis and evaluation of SAD, differential diagnosis of SAD, screening instruments for social anxiety disorder in adults, and treatment.