This review highlights advances made since 2004 in understanding the epidemiology of infection and the interactions between Ascaris lumbricoides and other concurrent infections. As water scarcity increases, untreated wastewater is increasingly used to irrigate crops, thus increasing the risk of transmission. New methods to detect and inactivate Ascaris eggs in water, soil and food are described. The association between pig ownership and Ascaris infection in humans may represent cross-transmission as hybridization among the pig and human ascarids occurs more frequently than previously believed. Geospatial analyses have successfully predicted infection levels both at a regional level (based on vegetation indices, temperature and humidity) and within communities (based on social and environmental factors). The interpretation of antibody and cytokine responses to Ascaris is becoming clearer, as researchers recognize the role of antigen type, age, the history of Ascaris and other infections. The considerable interest emerging on the interactions between Ascaris and other infections (helminths, malaria, HIV, tuberculosis) and allergy is explored. The impact of concurrent infection on the design of control strategies is discussed including the benefits arising from combination therapies and the evidence that intestinal nematodes impair the efficacy of childhood vaccines. Finally, recommended areas for future research are identified.