The frequency with which antimicrobial-resistant microorganisms are recovered from patients in health care settings, such as hospitals and nursing homes, is of great concern to those who manage and work in health care systems. 63 Such organisms have become increasingly frequent because of the presence of more patients with impaired host defenses, use of new instrumentation and procedures, decreasing resources for infection control, and the inability of some laboratory methods to detect novel resistance mechanisms. 41 Strains that have been consistently susceptible to all antimicrobial agents for decades now have developed resistance to those classic therapies. Other organisms have developed resistance to recent antimicrobials almost as soon as the drugs have been marketed. 13 Organisms that are resistant to several different groups of antimicrobials also have increased during the past few years. 62 These multidrug-resistant (MDR) microbes now cause an increasing number of infections each year. These infections formerly were seen primarily in the intensive care units (ICUs) of hospitals but now occur in other inpatient settings and even in ambulatory care. 1 In some cases, MDR strains have become so prominent that keeping patients with serious infections alive has become a difficult task, just as in the preantibiotic era. 24 As the magnitude of this problem continues to broaden, it is imperative that health care professionals become familiar with the causes of antibiotic resistance and the ways in which the emergence of resistance in bacteria can be prevented or minimized. This article highlights some of the factors leading to the development of resistance in organisms found in various parts of the health care system and the problems of control and prevention of the spread of these resistant bacteria in health care settings.