Cognitive Behavioral Therapy or Fluoxetine for Pediatric Anxiety

* INCLUSION CRITERIA: ALL JUVENILE SUBJECTS * Age: 8-17 (subjects who consent as 17-year-olds but turn 18 during the course of the study will be eligible to complete all procedures completed by other subjects who consent as 17-year-olds but do not turn 18). * Consent: can give consent/assent (Parents will provide consent; minors will provide assent) * IQ: all subjects will have IQ\>70 (Assessment relies on either a WASI or assessment by trained clinical staff during the subject s screening visit. Completion of required activities during the screening visit requires an IQ above 70.) * Language: all subjects will speak English (Tasks in this protocol have not been validated in languages other than English) ALL ADULT SUBJECTS * Age: 18-65 * Consent: can give consent * IQ: all subjects will have IQ\>70 (Assessment relies on either a WASI or assessment by trained clinical staff during the subject s screening visit. Completion of required activities during the screening visit requires an IQ above 70.) * Language: all subjects will speak English (Tasks in this protocol have not been validated in languages other than English) ALL SUBJECTS WITH AN ANXIETY DISORDER * Diagnosis: Current Diagnosis of OCD, Social Phobia, Separation Anxiety, Generalized Anxiety Disorder, or Panic Disorder (Based on K-SADS (juveniles) or SCID (adults)) * Symptom Severity: Clinically significant, ongoing anxiety symptoms (This will be documented by clinician review with patients and their families during at least two visits with families.) * Clinical Impairment: Clinically significant, ongoing distress or impairment from anxiety (This will be documented by clinician review with patients and their families during at least two visits with families.) ALL PREVIOUSLY ENROLLED ADOLESCENT PATIENTS, CHILD AND ADULT HEALTHY VOLUNTEERS, AND ALL HEALTHY VOLUNTEERS TURNED PATIENTS * Diagnosis: Current Diagnosis of OCD, Social Phobia, Separation Anxiety, Generalized Anxiety Disorder, or Panic Disorder; No current diagnosis (Based on K-SADS (juveniles) or SCID (adults)) * Clinical Impairment (as applicable): Clinically significant, ongoing symptoms (This will be documented by clinician review with patients and their families during at least two visits with families.) * Symptom Severity (as applicable): Clinically significant, ongoing symptoms (This will be documented by clinician review with patients and their families during at least two visits with families.) EXCLUSION CRITERIA: ALL SUBJECTS * Any serious medical condition or condition that interferes with fMRI or M/EEG scanning, and for patients electing medication, any condition that increases risk of SSRI treatment. (All patients will complete a medical history. Healthy volunteer participants will be medication- free and have no current serious medical conditions, based on a review of their medical history. Subjects only will be excluded from the MRI portions of the study based on this exclusion criterion.) * Pregnancy (Subjects only will be excluded from the MRI portions of the study based on this exclusion criterion.) * Current use of any psychoactive substance; current suicidal ideation as indicated by the presence of intent for engaging in suicidal behaviors; current diagnosis of attention deficit hyperactivity disorder (ADHD) of sufficient severity to require pharmacotherapy. (These factors could complicate treatment with an SSRI. No subject on medication will be accepted into the trial. Subjects will not be taken off of medications to enter the trial.) * Current diagnoses, major depressive disorder (MDD), post-traumatic distress disorder, conduct disorder. (These factors may be affected by SSRI treatment, influencing ability to detect effects on anxiety/symptoms of depression. Of note, subjects who present with a diagnosis of MDD will not be eligible for inclusion at the outset of the study. However, youth with anxiety disorders frequently develop MDD when followed over time. Subjects will be allowed to remain in the study if they develop these diagnoses after enrollment.) * Past or current history of mania, psychosis, or severe pervasive developmental disorder. (These factors may be affected by SSRI treatment, influencing ability to detect effects on anxiety/symptoms of depression. Of note, subjects who present with a diagnosis of MDD will not be eligible for inclusion at the outset of the study. However, youth with anxiety disorders frequently develop MDD when followed over time. Subjects will be allowed to remain in the study if they develop these diagnoses after enrollment.) * Recent use of an SSRI with failure to respond or tolerate SSRI treatment at an adequate dose and duration. (This is designed to exclude subjects who have failed a trial of an SSRI for their current problem with anxiety. For previously enrolled participants, including patients and healthy volunteers, current use of an SSRI does not exclude participation from follow-up research tasks.) * History of any (excepting nicotine-related and cannabis-related) DSM5-defined moderate to severe substance use disorder (or DSM-IV-defined substance dependence). HEALTHY ADULT SUBJECTS -Any current psychiatric diagnosis (Assessment relies on SCID)