Wheezing is a common physical finding in the pediatric age group 0-4 years and can have multiple diverse causes. Infectious causes are the most common culprit and lead to bronchiolitis or preschool asthma. The identification and understanding of these causes is fundamental in the appropriate treatment of our patients. The differentiation and underlying pathologies of these 2 conditions can be confusing and complicated. A systemic review of these conditions attempts to alleviate some of this confusion and tries to provide some clinical guidance for the treatment of these patients.