Acute viral respiratory infections (VRIs) encompass a range of illnesses that together constitute the most frequent infections of humans. The most prevalent syndrome is that characterized by signs and symptoms of the common cold, or acute viral rhinosinusitis. These illnesses are typically acute, self-limiting events associated primarily with upper respiratory symptoms, but they also cause symptoms that are indicative of lower respiratory involvement, particularly in the very young, the elderly, and those with preexisting airways disease. Rhinoviruses are the most common pathogen causing VRIs and account for approximately 50% of colds on an annual basis. Not surprisingly, the recent development of antiviral compounds with activity targeted against rhinoviruses has intensified interest in these infections. This supplement contains a series of articles based on presentations by internationally regarded experts who met on April 3 and 4, 2001 in Philadelphia, Pennsylvania, to discuss current knowledge and recent advances regarding the epidemiology, clinical impact, pathogenesis, and management of rhinoviral VRIs. Children get an average of 3 to 8 colds annually. Preschool children get an average of 5 to 7 per year, but 10% to 15% may get up to 12 per year. The incidence decreases with age to an average of about 2 to 4 colds per year by adulthood. Data from a survey conducted in 1996 by the National Center for Health Statistics reported that 62 million cases of colds required some form of treatment. This survey also showed that colds were associated with 148 million days of restricted activity, approximately 20 million days of missed work, 22 million days of missed school, and 45 million days during which individuals were bedridden. Gonzales et al reported that in 1998 there were 25 million office visits to primary care providers for upper respiratory tract infections. Furthermore, costs associated with the common cold have been estimated to exceed $3.5 billion per year in the United States. Another important factor contributing to the cost of VRIs is the use of antibiotics. Common colds and related VRI syndromes are among the most frequent reasons for inappropriate antibiotic use in the United States, which increases the costs of illness unnecessarily and contributes to the increasing prevalence of antibiotic-resistant bacteria. The Centers for Disease Control and Prevention estimates that about 50% of the approximately 100 million courses of antibiotics prescribed by office-based physicians each year are unnecessary. In 1994, it was estimated that more than 12 million antibiotic prescriptions were written annually for upper respiratory infections, at a cost of $37.5 million. In this regard, some of the common attributes of rhinovirus infection, discolored nasal discharge and postnasal drainage, are significantly associated with antibiotic prescribing. Furthermore, even though physicians are aware of the lack of benefit of antibiotics for these infections, surveys have shown that physicians were much more likely to prescribe antibiotics when they believed that their patients expected to receive them. However, physicians also overestimate the desire of their patients for an antibiotic. Given the substantial personal and societal impact of VRIs, the development of a safe and effective antiviral compound specifically targeted to the most common pathogen involved would represent a major advance in the field of respiratory infections. The picornavirus family includes important respiratory pathogens. The major groups causing VRIs are the rhinoviruses, which consist of more than 100 serotypes, and the enteroviruses, which comprise approximately 70 antigenic types. Rhinoviruses are the cause of about 50% of colds, and enteroviruses cause 5% to 15% of VRIs. Rhinoviruses are not only the primary etiologic agent in common colds; they also cause complications involving the upper and lower respiratory tract. These include otitis media, particularly in children; sinusitis; and exacerbations of asthma and other forms of airways disease, such as chronic obstructive pulmonary disease (COPD) and cystic fibrosis. –18 In addition, rhinoviruses can cause serious lower respiratory disease in certain populations, including infants and young children, elderly persons, and immunocompromised patients. Unfortunately, many clinical microbiology laboratories do not use optimal techniques to detect rhinovirus infections, so they remain underappreciated pathogens. These techniques, such as culture, are not available in a clinically useful timeframe. Also, recently developed polymerase chain reaction (PCR) techniques, which are the most sensitive for rhinovirus identification, are available only at research facilities. In this supplement, Dr. Arnold S. Monto begins with a review of epidemiologic studies that have assessed the From the University of Virginia School of Medicine, Charlottesville, Virginia, USA. Requests for reprints should be addressed to Frederick G. Hayden, MD, FACP, University of Virginia School of Medicine, Department of Medicine, PO Box 800473, Charlottesville, Virginia 22908.