Allergic or adverse reactions can occur at any time and to any type of contrast. A known history of an adverse reaction needs to be fully investigated, and a careful plan of care must be created for the patient prior to the administration of contrast. If patient experiences a reaction to contrast, the imaging team must be able to react quickly to provide appropriate care to the patient. This chapter helps the reader to identify the types of reactions. It discusses the emergency treatment of reactions and treatment of extravasation, as well as pretreatment for prior contrast reactions.