Lung ultrasound (LUS) is a point-of-care modality that can be effectively used in diagnostic and monitoring roles for patients with respiratory signs and symptoms. When performed in an organized and protocol-based fashion, LUS is accurate, reproducible, and repeatable. Its routine use has been shown to have substantial diagnostic and therapeutic impact. However, because of the unique interactions between ultrasound waves and aerated lung tissue, only a thorough and systematic approach, focusing on correct indications, proper image acquisition, and careful understanding and interpretation of both artifacts and anatomical findings, allows accurate sonographic diagnosis and integration with clinical data. In this chapter, we describe the ultrasound findings of normally aerated and injured lungs, review current available evidence for the most common lung pathologies, and suggest an intuitive framework and cognitive aid for a structured diagnostic approach to LUS.