The objective of this chapter is to introduce the lung ultrasonography. Transthoracic ultrasound (US) of the lungs is a useful diagnostic tool for pulmonologists, emergency and critical care physicians, or anyone interested in the evaluation of the lungs. Ultrasound is clearly useful in the diagnosis and characterization of pleural diseases like pneumothorax (PTX) and pleural effusion. Lung ultrasonography is a noninvasive clinical imaging technique that uses sound waves to evaluate thoracic structures. This chapter also discusses ultrasound equipment and probes, imaging of the chest wall, evaluation of pleural disease, study of diaphragmatic kinetics, evaluation of pulmonary disease and ultrasound-guided interventional procedures. Ultrasound can be used as a guide for interventional procedures, particularly for thoracentesis and chest tube insertion. The details of these invasive diagnostic procedures are covered in detail in this book.