First adopted in 1951, the International Health Regulations (IHR) provide the international legal framework for efforts to prevent and control the cross-border spread of communicable diseases. In 1995, after outbreaks of emerging infections had rendered the IHR increasingly obsolete, the 192 member states of the World Health Organization (WHO) requested a major updating of the regulations to adapt them to the highly mobile, globalized world of the 21st century. After negotiations in 2004 and 2005, the revised IHR text was adopted unanimously by the World Health Assembly, WHO's highest policymaking body. This article reviews the 2005 regulations and discusses their implications for the international response to natural epidemics and to incidents involving the accidental or deliberate release of biological or chemical agents or radiological materials.