Croup is an inflammation of the larynx and trachea most commonly caused by parainfluenza virus. It presents with inspiratory stridor, barking cough, and hoarseness in children ages 6 months to 3 years. The Westley Croup Score is used to evaluate severity, and treatment depends on score but may include dexamethasone, nebulized epinephrine, and hospitalization for severe cases. Differential diagnoses include epiglottitis, bacterial tracheitis, retropharyngeal abscess, and foreign body aspiration.