Anaphylaxis might be a severe, life-threatening emergency situation during surgical and medical procedures, caused by a hypersensitivity reaction to drugs, e.g. antibiotics or muscle relaxants, contrast agents or latex. This chapter will focus on clinical presentation, diagnosis, and immediate emergency treatment of suspected anaphylaxis to prevent progression to life-threatening respiratory and/or cardiovascular shock. Additionally, prevalence, risk factors, immunological mechanisms and prevention of recurrence are discussed, taking into account the current guidelines of the American Heart Association, the European as well as the British Resuscitation Council, the American College of Radiology and the European Society of Urogenital Radiology.