Anxiety and fear are evolutionary beneficial emotions that help an organism to avoid danger and threat, but anxiety becomes pathological when it significantly impairs daily functioning. Anxiety disorders are among the most prevalent psychiatric disorders, and both etiology (fear learning) and involved neural circuitry are relatively well understood. In this chapter, we discuss the potential of functional MRI in understanding and detecting pathological anxiety, with a specific focus on the role of fear conditioning and extinction as a prevailing experimental and etiological model.