This Phase 3 study is being conducted in North America, Argentina, and Brazil to evaluate the efficacy and safety of retigabine dosed at 1200 mg/day, in three equally divided doses, compared with placebo in patients with epilepsy who are receiving up to three established antiepileptic drugs (AEDs). The primary objective is to demonstrate a superior change in total partial seizure frequency for four weeks from baseline to the double-blind period. The proportion of responders (greater than or equal to 50% reduction in total partial seizure frequency for four weeks from baseline to the double-blind period) will also be evaluated.