Introduction Almost everyone knows what it feels like to be anxious or uncomfortable in a social situation. From surveys of many individuals from across the United States and elsewhere, Ruscio and his colleagues (2008) found that 40% of individuals considered themselves to be chronically shy, to the point of it being a problem. Another 40% reported that they had previously considered themselves to be shy. Fifteen percent more considered themselves to be shy in some situations, and only 5% reported that they were never shy. Social phobia (also called social anxiety disorder) is diagnosed when shyness or performance anxiety becomes so intense and so pervasive that it leads to clinically significant distress and impairment. As is reviewed later in this chapter, social phobia is one of the most prevalent psychological disorders. In this chapter we review the empirical literature pertaining to social phobia and social anxiety. We begin with a discussion of diagnostic issues and studies on descriptive psychopathology and epidemiology. Next, we review current theories and empirical evidence pertaining to both psychological and biological approaches to social anxiety. The paper concludes with an up-to-date review of psychological and biological treatments for social anxiety. Diagnostic Criteria and Description Social phobia is defined in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; American Psychiatric Association, 1994) as “a marked and persistent fear of one or more social or performance situations in which the person is exposed to unfamiliar people or to possible scrutiny by others. The individual fears that he or she will act in a way (or show anxiety symptoms) that will be humiliating or embarrassing (p. 416).” In addition to anxiety and fear related to social and performance situations, the individual must also  1. experience anxiety or fear almost every time he or she confronts the feared social situations,  2. recognize that the fear is excessive or unreasonable,  3. avoid the feared situations or endure them with intense anxiety or discomfort,  4. have had the problem for at least 6 months (only a requirement if the individual is under 18 years of age), and  5. experience significant distress and/or functional impairment resulting from the problem. Furthermore, the anxiety cannot be better accounted for by another mental disorder or be due to the direct effect of a substance or a general medical condition. Finally, if a general medical condition or mental disorder is present, the fear must be unrelated to it. Not all individuals with social phobia fear the same situations. In fact, the range of feared situations can vary from as few as one (e.g., a fear of public speaking) to as many as almost all situations in which other people are present. Subtypes of Social Phobia A number of subtyping strategies were considered when the DSM-IV was being developed. In their report to the DSM-IV subgroup on social phobia, Massion (2002) proposed three subtypes for the disorder:  1. circumscribed type (for people who fear only one or two situations),  2. generalized type (for people who fear most social situations), and  3. non-generalized type (for people who have clinically