Artemisinins are powerful drugs that have the most rapid action of all current drugs against Plasmodium falciparum, the parasite species that causes the most dangerous form of malaria. Artemisinin combination therapies (ACTs) are now standard treatment worldwide for P. falciparum malaria. Unfortunately, resistance to artemisinin has been detected in five countries across Southeast Asia. Along the Cambodia-Thailand border, P. falciparum is now resistant to most available antimalarial drugs. Artemisinin resistance poses a serious global threat to malaria control and elimination.