Inclusion Criteria:

• Subject has simple partial seizures (motor or sensory) or complex partial seizures (with motor manifestations) with or without secondarily generalized seizures.
• Subject has seizures that are distinct, stereotypical events that can be reliably counted, in the opinion of the investigator, by the patient or caregiver.
• Subject has seizures that are severe enough to cause injuries or significantly impair functional ability in domains including employment, psychosocial, education, and mobility.
• Subject failed treatment with a minimum of two antiseizure medications (used in appropriate doses) with adequate monitoring of compliance and the effects of treatment.
• Subject has remained on the same antiseizure medication(s) over the preceding three (3) months (independent of dose and other than acute, intermittent use of benzodiazepines).
• Subject has a minimum of four (4) or more countable seizures every month over the last three (3) months, as reported from the NeuroPace sponsored Prospective Seizure Frequency clinical investigation.
• Subject is > 18 years old and < 65 years old.
• Subject has undergone diagnostic testing that has established the epileptiform activity onset region(s) as part of his/her standard care to determine candidacy for epilepsy surgery.
• Subject is male, or if female is using a reliable method of contraception (hormonal, barrier method, surgical, or abstention), or is at least two years post-menopause.
• Subject or legal guardian is able to provide appropriate consent to participate.
• Subject can be reasonably expected to maintain a seizure diary alone or with the assistance of a competent individual.
• Subject is able to complete regular office visits and telephone appointments per the protocol requirements.
• Subject is willing to be implanted with a responsive neurostimulator (RNS) system as a treatment for his/her seizures.
• Subject is able to tolerate a neurosurgical procedure.
• Subject is considered a good candidate to be implanted with an RNS system.

Note: 1 month = 28 days

Exclusion Criteria:

• Subject has been diagnosed with psychogenic or non-epileptic seizures in the preceding year.
• Subject has been diagnosed with primarily generalized seizures.
• Subject has experienced unprovoked status epilepticus in the preceding year.
• In the opinion of the investigator, the subject has a clinically significant or unstable medical condition or a progressive central nervous system disease.
• Subject has been diagnosed with active psychosis, severe depression, or suicidal ideation in the preceding year.
• Subject is pregnant or planning on becoming pregnant in the next year.
• Subject is on the ketogenic diet.
• Subject was enrolled in a therapeutic investigational drug or device study in the preceding year.
• Subject has an implanted Vagal Nerve Stimulator (VNS).
• Subject has had therapeutic surgery to treat epilepsy in the preceding year.
• Subject is implanted with an electronic medical device that delivers electrical energy to the head or body.
• Subject is on chronic anticoagulants or, in the opinion of the investigator, subject is an unsuitable candidate for cranial surgery for any other reason.
• Subject had a cranial neurosurgical procedure in the previous month.
• Subject requires repeat MRIs.
• Subject's seizure onset zone(s) is/are located below the level of the subthalamic nucleus or, in the opinion of the investigator, the necessary lead placement would present too high a risk.

Note: Subjects who have had epilepsy surgery (resective, corpus callosotomy, or ablation) greater than one year ago are still eligible.