Acute thoracic symptoms are common among adults visiting emergency departments in the United States. Adults with these symptoms constitute a large burden on the overall resources used in the emergency department. The wide range of possible causes can make a definitive diagnosis challenging, even after clinical evaluation and initial laboratory testing. In addition to radiography and computed tomography, thoracic ultrasonography (US) is an alternative imaging modality that can be readily performed in real time at the patient's bedside to help diagnose many thoracic diseases manifesting acutely and in the trauma setting. Advantages of US include availability, relatively low cost, and lack of ionizing radiation. Emergency thoracic US consists of two main parts, lung and pleura US and focused cardiac US, which are closely related. Acoustic mismatches among aerated lungs, pleura, chest wall, and pathologic conditions produce artifacts useful for diagnosis of pneumothorax and pulmonary edema and help in detection of subpleural, pleural, and chest wall pathologic conditions such as pneumonia, pleural effusion, and fractures. Visual assessment of cardiac contractility and detection of right ventricular dilatation and pericardial effusion at focused cardiac US are critical in patients presenting with acute dyspnea and trauma. Additional US examinations of the inferior vena cava for noninvasive volume assessment and of the groin areas for detection of deep venous thrombosis are often performed at the same time. This multiorgan US approach can provide valuable information for emergency treatment of both traumatic and nontraumatic thoracic diseases involving the lungs, pleura, chest wall, heart, and vascular system. Online supplemental material is available for this article. (©)RSNA, 2016.