The application of molecular tools to the characterisation of the aetiological agents of echinococcosis has revealed a series of largely host-adapted species and genotypes that are maintained in distinct cycles of transmission. They can be defined on both genetic and phenotypic characteristics which complement previous observations made by descriptive parasitologists many years ago. A revised taxonomy for species in the genus Echinococcus has been proposed and widely accepted, particularly with respect to forms maintained in transmission cycles involving sheep, horses and cattle. However, molecular epidemiological studies are required in a number of endemic areas in order to determine cycles of transmission responsible for maintaining the parasite. The taxonomic status of forms in cervids, pigs and camels has still to be resolved, and the status and epidemiological significance of newly described species in China requires further research.