International travellers are often exposed to a wide range of infections, most of which are a reflection of common diseases in the destination country. The consequences of acquiring such infections are serious and can be associated with substantial morbidity and mortality. Attempting to define the range of infections and the risk factors that are associated with acquiring them during travel to different regions worldwide will provide an evidence base for the development and implementation of effective preventative interventions. This Science and Society article focuses on the valuable function served by the GeoSentinel surveillance network in defining the range of infections in travellers.