Transesophageal echocardiography (TEE) is a complementary technique to conventional echocardiography (TTE) and is used in patients in whom TTE reveals unsatisfactory image quality. The improved resolution in combination with the capability to visualize cardiac structures which are not detectable or poorly visualized by TTE has brought TEE into increasing use as a routine technique. TEE has been proven to be superior to TTE for various indications, e.g., detection of infective vegetations or perivalvular abscesses, evaluation of acute chest pain or potential embolic sources, evaluation of prosthetic valve function, evaluation of hypotensive or hypoxic patients, intraoperative monitoring of LV function or control of surgical results after correction of complex congenital heart disease or mitral valve reconstruction. TEE is an semi-invasive technique which can be performed in > 95% of patients with only minor discomfort; life threatening complications are rare (< 0.1%). TEE is a bed-side and low-cost technique which can be rapidly applied in the operation room as well as intensive care unit. TEE combines functional and morphological data with a high diagnostic accuracy and may be, therefore, an important diagnostic tool also for the next millennium despite new developments in alternative imaging techniques such as magnetic resonance.