A mug is a sturdily built type of cup often used for drinking hot beverages, such as coffee, tea, or hot chocolate. Mugs, by definition, have handles and often hold a larger amount of fluid than other types of cup. Usually a mug holds approximately 12 fluid ounces (350 ml) of liquid; double a tea cup. In formal settings a mug is usually not used for serving hot beverages, with a teacup or coffee cup being preferred. Shaving mugs can be used to assist in wet shaving.

Whereas ancient mugs were usually carved in wood or bone or shaped of clay, most modern ones are made of ceramic materials such as earthenware, bone china, porcelain or stoneware. Some are made from strengthened glass, such as Pyrex. Other materials, including plastic, steel and enameled metal are preferred where break resistance and reduced weight are at a premium, such as for campers. Techniques such as silk screen printing or decals are used to apply decorations; these are fired onto the mug to ensure permanence.