Medical imaging plays an important role in medical communication and education as well as research. X-ray, computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI), and positron emission tomography (PET) are most commonly used medical techniques. Most of them provide good resolution but each of them has some limitations. For example, X-ray can cause radiation, poses a health risk and it is less informative when it comes to imaging soft tissues. MRI is very expensive, further internal body movements such as heartbeat can produce measurement artifacts in an MRI image. Moreover, there may also be a chance of a false alarm when using these imaging techniques for tumor detection. This chapter reviews the existing medical imaging techniques, applications and limitations.