In late 2007 local and national news outlets covered MRSA outbreaks in day care centers and high school locker rooms, highlighting what appeared to be a new and spreading epidemic. Next came the warning that C. diff may be the “next MRSA.” Within a year, though, media coverage on these threats has waned. Did the threat of antibiotic resistance vanish as quickly as it faded from the public’s sight, or is it a continuing problem that still deserves public attention and resources? Understanding the scale of the antibiotic resistance problem is the first step in crafting effective solutions. Developing hospital infection control plans requires knowledge about the number of resistant cases in different hospital units and geographic areas. Finding new and useful antibiotics requires identifying drug targets that will yield improved results for patients. Creating an antibiotic stewardship program requires understanding the number of infections that do and do not respond to available treatments. The papers featured in this section estimate the number and type of infections caused by different organisms, which forms a foundation for subsequent work.