Oral and Intravenous contrast is often needed in both MRI and CT scans to evaluate anatomical and pathological processes involving the gut, blood vessels, in the evaluation of vascular lesions and for vascular mapping in transplant patients. It is also needed in trauma patients, in studying response to treatment and in patients having active and profuse bleeding from any where in the body. Therefore, it is essential to know about contrast medium which are used in imaging studies. The CT contrast is iodine based while MR contrast is gadolinium based. While both contrasts have clinical uses, it must also be remembered that they can have side effects ranging from minor to very severe side effects. In this chapter, we will briefly view the various types of contrasts used in daily clinical practice.