Chikungunya, dengue, yellow fever and Zika viruses share many attributes. All are complex and widespread zoonoses of subhuman primates that have made successful transitions to the urban Aedes aegypti transmission cycle. More important, they have an established record of travelling, having moved from their place of origin hundreds of years ago, sometimes repeatedly. Understanding their epidemiology requires a knowledge of past behaviors including unexplained restraints to their travel. This is a review of mechanisms that may contribute to invasiveness and pathogenicity of these important human pathogens.