To better understand the epidemiology of ascariasis, molecular genetic methods have been applied to differentiate between worms found infecting people and pigs, and other occasional hosts. Owing to difficulties in applying species concepts, the longstanding debate of the distinction(s) between Ascaris lumbricoides and Ascaris suum continues. From an applied perspective, however, molecular markers help to "tag" and "track" worms during their transmission cycle(s), providing new insights into host range, as well as methods for assessing parasite population dynamics through time and contingent upon disease control. While useful in determining dynamics at the tips of the evolutionary tree, these molecular tools also provide insights into deeper evolutionary branches. Although Ascaris is found throughout the globe, molecular analysis of worms retrieved from sub-Saharan Africa point towards a significant center of genetic diversity, possibly denoting a likely center of evolutionary origin with subsequent parasite diaspora. Resolving these issues precisely, however, requires greater scrutiny of genetic variation within Parascaris and Baylisascaris. © 2013