Wheezing is a whistling sound that occurs with expiration due to narrowing or obstruction of the small airways. Up to 50% of children experience recurrent episodes of wheezing by age 5 years. Diagnosis of the cause can be difficult because of the many possible etiologies. The history should include the family history, age of onset, and pattern of wheezing (transient vs persistent). The differential diagnosis varies depending on age of onset, with younger children more commonly experiencing wheezing caused by congenital abnormalities or viral etiologies. Gastrointestinal reflux disease is another cause of wheezing in younger children. Children older than 1 year may experience wheezing related to acute processes including viral illness, foreign body aspiration, and reactive airways. The most common causes of wheezing in children younger than 6 years are bronchiolitis and asthma. A parental history of asthma, allergies, or eczema increases a child's likelihood of developing asthma. There are associations between wheezing and obstructive sleep apnea and snoring in children. Evaluation of wheezing should be guided by the patient history and presentation. Chest radiography is recommended as the initial imaging study for those with recurrent episodes of wheezing without a clear etiology. Management is determined by the underlying etiology.