Recently, global health and global health surveillance have received unprecedented recognition of their importance because of the newly emerging and reemerging infectious diseases, new cycles of pandemics, and the threats of bioterrorism. The aim of this review is to provide an update of the current state of knowledge on health surveillance in a globalized world. Three key areas will be highlighted in this review: 1) the role of the new International Health Regulations, 2) the emergence of new global health networks for surveillance and bioterrorism, and 3) the reshaping of guidelines for the collection, dissemination, and interventions in global surveillance. A discussion is also presented of the more important challenges of global health surveillance. Global surveillance has been reshaped by important changes in the new International Health Regulations and the rapid development of new global networks for disease surveillance and bioterrorism. These networks provide for the first time at the global scale real-time information about potential outbreaks and epidemics of newly emerging and reemerging infectious diseases. The recent outbreaks of severe acute respiratory syndrome (SARS) and the influenza A (H1N1) pandemic provide evidence of the benefits of the new global monitoring and of the importance of the World Health Organization in its coordinating role in the multilateral response of the global public health community.