The small airways of the lungs are an often misunderstood and confusing anatomic location teeming with an array of similar-appearing disease processes that can be daunting even to the most experienced radiologist. This article shows that an understanding of small-airway anatomy and accurate pattern recognition can allow one to determine useful clinical differential diagnoses. The ability to recognize mosaic lung attenuation, and the presence of centrilobular nodules and reticular opacities (tree-in-bud), with or without ground glass, is of critical importance in evaluating this portion of the lung. In addition, we attempt to further show how high-resolution computed tomography (HRCT) scanning has opened the deep recesses of the lung to the thoracic radiologist, allowing for a more meaningful radiologic contribution to the clinical care of patients with unexplained pulmonary symptomatology.