Gastroesophageal reflux (GER) disease is the most common disease of the gastrointestinal tract that is met with in pulmonary practice. Silent GER is common. This chapter discusses the pathophysiology of reflux and its possible contribution to lung disease. It distinguishes between the mechanisms of gastroesophageal reflex as opposed to reflux, and discusses the entity of gaseous reflux. It also elucidates the symptoms that may point to GER as the cause for a persistent cough. It explores the pulmonary conditions associated with GER and attempts to correlate symptoms with the underlying pathophysiology in each instance, emphasising the reciprocal relationship between GER and lung disease. It also outlines the available tests for the diagnosis of GER. The chapter also includes a discussion on the inflammatory bowel diseases (Crohn’s disease and ulcerative colitis) and explores the effect of each on the various compartments of the lung.