The journal Nature offers this free Web focus on Severe Acute Respiratory Syndrome (SARS), in which "Nature's reporters pose key questions about the outbreak, and assess our preparedness to deal with future viral threats." Reader will find dozens of articles, including editorials, Science Updates, and Brief Communications from the journal. The articles trace the chronology of the SARS epidemic, and the section titled "What Have We Learned?" offers an excellent overview of what we know and what remains to be seen.