Acute and emergency physicians need to make rapid and far-reaching decisions on the basis of little diagnostic information. In patients with symptoms suggestive of a cardiopulmonary diagnosis, point-of-care lung ultrasound (LUS) is becoming increasingly used. In patients with acute dyspnea, chest pain and shock, LUS increases the diagnostic reliability. The BLUE protocol helps to differentiate important diagnoses of acute dyspnea (pulmonary edema, pneumonia, acute respiratory distress syndrome, pulmonary embolism, pleural effusions or pneumothorax). LUS is also used for treatment follow-up. It is clearly superior to other diagnostic measures (auscultation, chest X‑ray). With ever smaller "handheld" ultrasound devices, the use of ultrasound is also being increasingly used in preclinical situations.