A sommelier or wine steward is a trained and knowledgeable wine professional, usually working in fine restaurants and specialises in all aspects of wine service as well as wine and food matching. The sommelier role is more specialized and informed than that of a waiter, maitre d' or wine waiter.

The key role of a sommelier is in the areas of wine procurement, wine storage, cellar rotation, and expert service to wine customers. A sommelier may also be responsible for the development of wine-lists and for the delivery of wine service and training for other restaurant staff. Also preferably working with the chef, to pair and suggest wines that will best complement each particular dish on the menu. This requires the need for a deeper knowledge of how food and wine, beer, spirits and other beverages work in harmony with cuisine.

A professional sommelier also works on the floor of the restaurant and is in direct contact with restaurant guests. The sommelier has a responsibility to work within the taste preferences and budget constraints of the customer. In some situations, a sommelier's role may be broader than simply working only with wines, and may encompass all aspects of the restaurant's service, with an enhanced focus on wines, beers, spirits, soft-drinks, cocktails, mineral waters and even tobaccos.

Though sommelier is a title potentially anyone may claim, becoming a certified sommelier requires classes and an examination. The Court of Master Sommeliers, established in 1977, is the examining body for the Master Sommelier Diploma, Advanced Sommelier Certificate, Certified Sommelier Certificate and the Introductory Sommelier Certificate and was created under the guidance of the Vintners Company, The Institute of Masters of Wine, The British Hotels & Restaurants Association, The Wine & Spirit Association of Great Britain and The Wholesale Tobacco Trade Association. Since the Master Sommelier Diploma was introduced in 1969, approx. 180 people around the world have become Master Sommeliers by 2011.