Endoscopic ultrasound (EUS) has become important in a variety of clinical settings. Echoendoscopes may be categorised into radial and linear configurations. Radial devices are used for diagnostic imaging, whereas linear echoendoscopes also facilitate image guided tissue sampling and intervention. EUS is an established primary diagnostic tool for a number of conditions including choledocholithiasis and biliary microlithiasis. It is therefore well suited to the investigation of the aetiology of pancreatitis where simpler measures fail to identify the aetiology. It can also be used to identify chronic non-calcific pancreatitis. EUS is important in the secondary evaluation of abnormalities detected by other imaging modalities-for example, cystic pancreatic lesions. The high resolution of EUS allows more detailed image based analysis than other imaging modalities. The ability to sample cyst fluid significantly increases the accuracy of lesion characterisation. Most importantly, EUS has become indispensable in the staging of a variety of upper gastrointestinal tract tumours. If resection is being considered, the high resolution images obtained via EUS are invaluable for local tumour staging. EUS guided tissue sampling permits accurate nodal staging without relying on lymph node size as proxy for malignant infiltration. In patients with contraindications to magnetic resonance imaging, EUS is an alternative for the staging of rectal carcinoma. It is used in the staging of lung cancer, often in combination with endobronchial ultrasound. Finally, EUS is used therapeutically in image guided drainage (such as gastrocystostomy in pancreatic pseudocyst) and coeliac plexus neurolysis in patients with abdominal pain caused by pancreatic cancer or pancreatitis.