Vagus Nerve Stimulation Clinical Outcomes Measured Prospectively in Patients Stimulated

Inclusion Criteria: Patients enrolled in the study must meet all of the following criteria at Visit 1: (Baseline) if Screening Incl/Excl is omitted: 1. Patients must agree to be treated with VNS Therapy. The decision to treat with VNS Therapy must have been made independent of and prior to participation in the study. 2. Patients participating at Sites not located in the US must follow the "Non-US" labeling and be at least 7 years or older and whose epileptic disorder is dominated by partial seizures (with or without secondary generalization) or generalized seizures that are refractory to antiepileptic medications; patients participating at Sites located in the United States must be 12 years or older and have partial onset seizures or must follow the indication for use statement (for VNS Therapy) in the country of origin. 3. Patient and/or caregiver must be able to give accurate seizure counts, health outcomes information, and complete study instruments with minimal assistance. 4. Patient or legal guardian understands study procedures and voluntarily signs an informed consent and in the United States a Health Insurance Portability and Accountability Act (HIPAA) authorization in accordance with institutional policies. In the event that the patient is under the age of 18 the patient will also be required to sign an assent affirming their agreement to participate in research according to local IRB requirements. Similar authorization is required per EC requirements, or equivalent authority. Additional Continuation Criteria to be evaluated at Visit 2 (Baseline): 5. Patient must be taking at least 1 anti-epileptic drug treatment and stable on said medications for at least 8 weeks (56 days) prior to baseline. (Rescue medication may be allowed on a case-by case basis with Cyberonics approval.) 6. Patient must have a minimum frequency of 3 seizures (excluding absence seizures, simple partial seizures and myoclonic jerks) per month (average over 2 months) prior to baseline; maximum frequency is 20 seizures per day. 7. Patient must have no more than 4 weeks between seizures (over 2 months) prior to baseline. Exclusion Criteria: Patients with any of the following will not be eligible for enrollment: 1. Patient currently uses, or is expected to use during the study, short-wave diathermy, microwave diathermy, or therapeutic ultrasound diathermy. 2. Patient is expected to require full body magnetic resonance imaging during the clinical study. 3. Patient has a progressive neurological condition (e.g. brain tumor etc.). 4. In the investigator's opinion, the inability of the patient, legal guardian or reluctance of the child to comply with the frequency of clinic visits during the treatment phase. 5. In the investigator's opinion, the patient has a history of noncompliance for seizure diary completion. 6. Patient is currently using an investigational device or pharmacologic medication not approved by either EU or US regulatory authority. 7. Patient has had a previous VNS Therapy implant. 8. In the investigator's opinion, the patient is suicidal.