This study will evaluate the effects of Mindfulness-Based Stress Reduction (MBSR) on physiological reactivity. This study will focus on individuals with anxiety who will participate in an 8-week MBSR class. The investigators will test participants' reactivity to both predictable and unpredictable stimuli before and after the class to understand the physiological changes that may occur after to the intervention. Secondary measures include psychometric instruments and a delay discounting task.

Mindfulness-Based Stress Reduction (MBSR) is a manualized, systematic training in mindfulness meditation that has been found to have beneficial health effects, such as decreased stress and anxiety. The current protocol aims to examine the effects of MBSR on several physiological and behavioral measures in people with anxiety disorders, which may help us understand the effects of the intervention on anxiety. The investigators will use the NPU task as developed by the NIH, which measures an individual's response to threatening stimuli (mild shock) paired with non-threatening stimuli (geometric shapes). Individuals with anxiety disorders will be recruited to participate in this study, and will be randomized to a control (waitlist) or MBSR intervention group. Other secondary measures will examine the effects of mindfulness meditation on decision-making, and stress and anxiety symptoms.

Inclusion Criteria:

1. Men and women from 18-65 years of age.
2. Have an anxiety disorder, including: social anxiety disorder (SAD), generalized anxiety disorder (GAD), panic disorder, posttraumatic stress disorder (PTSD), agoraphobia, or simple phobia.
3. Must understand study procedure and willing to participate in 2 testing visits, and MBSR course as assigned.
4. Participants must be able to give informed consent to the study procedures.

Exclusion Criteria:

1. Subjects experiencing a current depressive episode or other axis I psychiatric disorders such as psychotic disorders, obsessive compulsive disorder, current eating disorders, bipolar disorder, and current substance use disorders.
2. Lack of measurable eye blink/eye twitch response (3 times the baseline eye blink muscle activity as measured by electromyography) for at least 5 of 9 startles used during the habituation visit.
3. A serious medical condition that may result in surgery or hospitalization.
4. Subjects who will be non-compliant with the study procedures. This may include planned travel out of town.
5. Women who are pregnant.
6. Current evidence of median nerve entrapment or carpal tunnel syndrome.
7. Subject who has resting blood pressure outside of a systolic blood pressure range of 90-140 mmHg, or a diastolic blood pressure outside a range of 50-90 mmHg on two consecutive measurements, taken up to 10 minutes apart.
8. Subjects taking benzodiazepines, barbiturates, antidepressants, antipsychotics, or sedative medications
9. Subjects currently receiving concomitant psychotherapy directed at treating anxiety symptoms (i.e. CBT).
10. Individuals with implanted electronic devices, such as a cardiac pacemaker.
11. Individuals who have completed a full course of MBSR, an equivalent meditation training, or have a daily meditation practice.

Since this study is focusing on a mind-body skill as a treatment it will be impossible to mask the participant.