The interpretation of a chest X-ray not only requires a methodical approach but also basic clinical and radiological knowledge for the interpretation of different findings. One fundamental observation common to all diseases is that they can replace air within the air spaces, and thicken the supporting lung architecture, thereby distorting the normal arrangement of the lung tissues, and making the normally invisible matrix visible. They can affect blood vessels, pleura, diaphragm, mediastinal structures and bones in various ways. To these observations, which can be shared by all diseases, by adding clinical and laboratory data, one tries to tease out a diagnosis from the list of differential diagnoses.