Radiation exposure to the patient has become a concern for the radiologist in the multidetector computed tomography (CT) era. With the introduction of faster multidetector CT scanners, various techniques have been developed to reduce the radiation dose to the patient; one method is automatic exposure control (AEC). AEC systems make use of different types of control, including patient-size AEC, z-axis AEC, rotational or angular AEC, or a combination of two or more of these types. AEC systems operate on the basis of several methods: standard deviation, noise index, reference milliamperage, and reference image. A clear understanding of how to use different AEC systems on different multidetector CT scanners will allow users to modulate radiation dose, reduce photon starvation artifacts, and maintain image quality throughout the body. Further development of AEC systems and their successful introduction into clinical practice will require user education and good communication between users and manufacturers.