Problems with cognition are common in patients with epilepsy. A series of double-blind, randomized, crossover, healthy volunteer studies have been conducted to avoid a variety of the confounding effects on cognition such as those produced by changes in seizure frequency. All of the older AEDs produced cognitive effects compared to the non-drug conditions. The cognitive effects of several of the new AEDs are described although data are limited. Studies have demonstrated that in utero AED exposure in humans may affect cognitive development. Although the cognitive effects of AEDs are generally modest, these effects can have clinical significance. The available data suggest that some of the new AEDs have fewer effects on cognition and memory than the older AEDs, and these differences can have clinical impact.