Pneumonia is a serious medical condition and a major cause of morbidity and mortality worldwide. It has many infectious aetiologies, although bacterial and viral forms are most common. Our understanding of pneumonia has improved significantly during the course of the 20th century but the overall disease burden has changed little. Although antibiotics have helped to reduce the mortality associated with some types of pneumonia, the level of morbidity remains constant. Furthermore, the existence of antibiotic-resistant bacteria worldwide is becoming an increasing problem in treatment. This essay describes the different types of pneumonia from a clinical perspective and highlights the problems associated with the condition.