Artemisinin comes from the plant, Artemisia annua, an ancient Chinese herbal remedy for relapsing fever. Rediscovery of its antimalarial action in China in the 1970s has seen it and its semisynthetic derivatives become the most useful drugs for most malarial illness. Artemisinins have a sesquiterpene lactone structure. Their anti-microbial action relates to a characteristic endoperoxide moiety. The precise mechanism of action remains controversial. Experimental induction of parasite resistance both in vitro and in vivo has been followed by recent initial clinical reports of resistance. Artemisinins are currently preferred as parenteral treatment of severe malaria, pre-referral rectal treatment and, as part of artemisinin combination therapy (ACT) oral treatment of uncomplicated falciparum malaria. Currently, amongst the most widely used drugs in the world, their future will be determined by the rate and extent of development of resistance. Better understanding of mechanisms of action and resistance and policy initiatives to prevent or delay resistance will be crucial.