Several population-based birth cohort studies documented that 30% of children suffer from wheezing during respiratory infections before their third birthday. Infants are prone to wheeze because of anatomic factors related to the lung and chest wall in addition to immunologic and molecular influences in comparison to older children. Viral infections lead to immunologic derangements that cause wheezing both in immunocompetent and immunodeficient infants. Anatomic causes of wheeze may be extrinsic or intrinsic to the airway. Not every wheeze is indicative of asthma but prediction of asthma in persistent wheezers is possible. Testing for allergy in these infants is worthwhile and can be of significant value in avoidable allergens. Treatment of an infant with wheezing depends on the underlying etiology. Response to bronchodilators is unpredictable and a trial of inhaled steroids may be warranted in a patient who has responded to multiple courses of oral steroids, has moderate to severe wheezing, or a significant history of atopy including food allergy or eczema. Ribavirin administered by aerosol, hyper-immune respiratory syncytial virus immunoglobulin (RSV IVIG), and intramuscular monoclonal antibody to an RSV protein have been used for RSV bronchiolitis in infants with congenital heart disease or chronic lung disease.