After a hiatus of almost 20 years, nine new antiepileptic drugs were licensed during the last decade of the 20th century. Expansion of the range of drug treatments for epilepsy complicates selection of the most suitable drug, or combination of drugs, for individual patients. Clinical experience suggests that mechanism of action may become an important criterion in this decision-making process. At the cellular level, three major pharmacological actions are recognised: modulation of voltage-dependent ion channels, enhancement of inhibitory neurotransmission, and attenuation of excitatory transmission. This review provides an update on the principal mechanisms of action of a range of established and modern antiepileptic drugs.