Gastric emptying is central to the pathophysiology and rational management of diabetes (T1D, T2D and pancreatogenic): This recognition represents a paradigm shift where recent research has refuted long-established dogma. Gastric emptying should be measured using a precise technique. Scintigraphy (radioisotopically-labelled meals and a gamma camera) developed in the 1970s, remains the ‘gold standard’ method. The stable isotope breath test is simpler and an acceptable alternative. The paracetamol absorption test (plasma kinetics of an oral paracetamol dose) is used widely, but has major limitations. Gastric emptying is delayed (gastroparesis) in 30-50% of individuals with longstanding, poorly controlled T1D or T2D (often modestly). Conversely, in well controlled T2D (and obesity without T2D), gastric emptying is often more rapid. Contrary to expectations, the association of symptoms, such as nausea and vomiting, with gastroparesis is poor and the effect of pharmacologically or surgically-induced acceleration of emptying on symptoms only modest. Gastric emptying is a major determinant of postprandial glucose, accounting for 30-40% of the variance in the initial glycaemic response to carbohydrate. In insulin-treated T1D or T2D gastric emptying affects postprandial insulin requirement and gastroparesis may predispose to hypoglycaemia. Insulin-induced hypoglycaemia accelerates gastric emptying and probably represents an important counter-regulatory mechanism. Gastric emptying is a major determinant of postprandial blood pressure – postprandial hypotension (fall in systolic blood pressure >20mm Hg) occurs frequently in diabetes and is an underappreciated, cause of morbidity, particularly falls. Both ‘short’ and ‘long-acting’ GLP-1RAs, used widely in the management of T2D slow gastric emptying to diminish postprandial glycaemic excursions and the fall in blood pressure. Marked slowing of gastric emptying by GLP-1RAs may lead to prolonged intragastric retention of food to increase the risk of aspiration at the time of surgery or upper gastrointestinal endoscopy. More information is required to inform guidelines for the use of GLP-1RAs before procedures.