Transesophageal echocardiography (TEE) has a key role in evaluation of cardiac valvular lesions, the left atrium or its appendage, atrial septal defects, intracardiac masses, endocarditis and its complications, and thoracic aortic lesions such as aortic dissection. Patients with atrial fibrillation undergo direct-current cardioversion without preceding chronic anticoagulation if TEE does not show intracardiac thrombi. With ablation procedures, atrial fibrillation has become one of the most common reasons for TEE referrals. The crucial role of TEE in the operating room has been established to assess the result of various valvular repair, and in the catheterization laboratory to guide interventional procedures. In this chapter, we will review the indications and contraindications of TEE as well as its standard views and necessary preparations.