Therapeutic drug monitoring (TDM) is widely accepted as a method to improve the effectiveness and safety of the first generation antiepileptic drugs (AEDs) and to identify an individual's optimum concentration. Like the older AEDs, the new AEDs also have significant pharmacokinetic variability. A similar relationship between concentration and effect for the new and old AEDs in experimental seizure models suggests that it is reasonable to use TDM for the new AEDs. With the addition of generic formulations of the new AEDs, TDM can play an important role to validate bioequivalence in patients. There is a history of problems with generics of the older AEDs, primarily carbamazepine and phenytoin. The Biopharmaceutics Classification System, which correlates the solubility and permeability of a drug with oral drug absorption, predicts that there should be no significant problems with the majority of the new AEDs. Because of the controversy over the risk-benefit of generic substitution of AEDs, the use of TDM will provide a way to ensure patient safety while establishing that generics of AEDs proven to be bioequivalent in population studies are also bioequivalent in individuals. The goal of personalized medicine is to use genetic testing to target therapy and identify those individuals unlikely to respond to a drug or likely to respond adversely to the same drug. Of all the AEDs, only phenytoin undergoes significant metabolism by cytochrome P450 isozymes with significant genetic polymorphisms (CYP2C9, CYP2C19). Studies are still needed to identify genetic and biomarkers to identify patients at risk for serious idiosyncratic reactions. There have been significant advances in the understanding of the role of genetics in idiopathic as well as acquired epilepsies. Identification of experimental and clinical evidence linking functional changes associated with gene mutations to epilepsy syndromes will help provide new molecular targets for future AEDs.