Viruses remain one of the greatest public health challenges, causing an amazing variety of diseases and increasingly threatening deadly, globe-spreading pandemics like Ebola. Viruses also cause at least 15% of human cancers, are suspected to contribute to neurological other chronic diseases, and are rising as bioterrorism threats. New pathogenic viruses like HIV, MERS, Zika, etc. are emerging at an accelerating pace, driven by increasing human population density, wild habitat encroachment, phenomenal viral mutation rates and other trends. In parallel, viruses are a major source of insights into normal cell biology, and provide expanding tools for biomedicine, biotechnology and nanotechnology.