Today's world of travel helps even the tiniest of organisms--microbes--find their way to new environments. Influenzavirus A, or Avian influenza (also known as bird flu), which originated in Asia, is steadily making its way to new countries as a result of commerce, and experts anticipate a pandemic. This well-timed resource goes beyond the headlines in explaining the potentially devastating impact of invasive viruses, bacteria, protists, and fungi. The author evaluates scenarios for success in the escalating battle for containment.