On November 8, 1895, Wilhelm Conrad Röntgen, a German scientist, began observing and documenting X-rays while experimenting with vacuum tubes.The modern medical X-ray tube was invented in 1913 by American scientist, William Coolidge.

X-rays are a form of electromagnetic radiation, just like visible light. In a health care setting, x-rays are emitted by a machine as individual "particles" (photons) that pass through the body and then get detected by a sensitive film. Structures that are dense (such as bone) will block most of the photons, and will appear white on developed film. Structures containing air will be black on film, and muscle, fat, and fluid will appear as shades of gray. Metal (such as silver fillings) blocks almost all the photons and will appear bright white.

X-rays have long been used in medicine as they are especially useful in the detection of pathology of the skeletal system, but are also useful for detecting some disease processes in soft tissue. Notable examples are the chest X-ray, which can be used to identify lung diseases such as pneumonia and lung cancer, the mammography, used to detect breast cancer, and the abdominal X-ray, which can detect blockage of the intestine.

The test is performed by positioning the patient in one or more positions before the X-ray device. Exposures are brief; less than 1 second.