The most immediate and widely feared infectious disease threat is the global spread of a highly contagious, unknown and dangerous agent. The prospect has become increasingly realistic in this era characterized by high-speed international travel – in a matter of hours, we can move from one continent to another over thousands of miles away. Even the most rapid infectious diseases require six hours from the time of infection to the manifestation of illness. Most agents require a longer period of days, months or even years. This means that we can be infectious before we really know we are ill. We can bring new infections into communities that are naïve to those infections. This is not new; travelers introduced and spread syphilis through Europe in the 18th and 19th centuries, and adventurers and explorers caused great epidemics in the Americas when they introduced measles and smallpox. The great plague of the 14th century is thought to have arrived in Europe via traders traveling from Asia. But now things are faster. Time increasingly is not on the side of public health and safety. In this chapter, we discuss the relationship between travel and emerging disease and examine two new challenges: SARS and avian influenza. The lessons they bring about the new era of the global express are sobering.