A-line pattern strongly correlates with dry pulmonary interstitium, low pulmonary capillary wedge pressure, and therefore, low likelihood of cardiogenic pulmonary edema. B-line artifacts are nonspecific markers of subpleural interstitial thickening with a broad differential. A B-line predominance is characteristic of pulmonary edema, acute respiratory distress syndrome, interstitial lung diseases, pneumonia, pneumonitis, pulmonary infarcts, and pulmonary contusions. Various protocols, algorithms, and scoring systems have been developed utilizing A-line and B-line patterns to help elucidate the underlying etiology of patients’ respiratory failure.