The diagnosis of indeterminate mediastinal lymph nodes, masses, and peripheral pulmonary nodules constitutes a significant challenge. Options for tissue diagnoses include computed tomography-guided percutaneous biopsy, transbronchial fine-needle aspiration, mediastinoscopy, left anterior mediastinotomy, or video-assisted thoracoscopic surgery; however, these approaches have both advantages and limitations in terms of tissue yield, safety profile, and cost. Endobronchial ultrasound (EBUS) is a new minimally invasive technique that expands the view of the bronchoscopist beyond the lumen of the airway. There are two EBUS systems currently available. The radial probe EBUS allows for evaluation of central airways, accurate definition of airway invasion, and facilitates the diagnosis of peripheral lung lesions. Linear EBUS guides transbronchial needle aspiration of hilar and mediastinal lymph nodes, improving diagnostic yield. This article will review the principles and clinical applications of EBUS, and will highlight the role of this new technology in the diagnosis and staging of lung cancer.