This chapter provides detail description of bronchiolitis. Chapter has 5 well illustrated diagrams and pictures. Bronchiolitis, virus causing bronchiolitis, predisposing factors, scoring system to assess severity, correlation between respiratory syncytial virus (RSV) infection and wheezing, prevention are described in detail. One table is added to highlight scoring system to assess the severity of the patient’s condition. One box is included to depict indications for Pallvizumab. 5 references are included at the end of the chapter to facilitate further reading.