By definition, inflammation of the lung parenchyma is called pneumonitis, and if the cause of that inflammation is a microbial agent, it is called pneumonia. Microbial agents can be bacterial, viral, or even parasitic agents. According to the WHO definition, IMCI (Integrated Management of Children's Illness) project, clinically, pneumonia is an acute attack of cough with or without fever, which is accompanied by difficulty breathing or increased breathing rate (tachypnea). After the successful implementation of the control and treatment program for acute gastrointestinal infections and gastroenteritis caused by it, acute respiratory infections and especially pneumonia are considered the most important infectious cause of death of children in developing countries in recent years. Pneumonia diagnosis is mainly a clinical diagnosis that can be divided into three categories bacterial, viral, and acute pneumonia based on four criteria clinical, epidemiology, radiology, and routine laboratory findings. In each case, based on the characteristics of that pneumonia, a possible diagnosis is given and the corresponding treatment is carried out. The correct and accurate knowledge of doctors on how to diagnose and treat this important disease in children without spending extra costs can play a fundamental role in preventing and reducing its mortality and morbidity.