Anxiety disorder is likely caused by an interaction of multiple loci in brain, rather than a single locus. Hyperactive neurotransmitter circuits between the cortex, thalamus, amygdala, and hypothalamus are responsible for production of anxiety symptoms. Familial studies performed on anxiety disorder suggested that anxiety disorder should be caused by genetic etiology. Numerous linkage and association studies showed different genetic loci of anxiety disorder. Candidate genes have been focused on important neurotransmitters, neuropeptide, or genes affecting neuronal growth, development, protection or apoptosis. Anxiety disorder has various symptoms and comorbid diseases in family or proband. Therefore, further studies focused on symptomatic dimension of anxiety disorder or responses to drugs are required.