Gueuze (or Geuze) is a type of lambic, a Belgian beer. It is made by blending young (1-year-old) and old (2- to 3-year-old) lambics, which is bottled for a second fermentation. Because the young lambics are not fully fermented, the blended beer contains fermentable sugars, which allow a second fermentation to occur. Lambic that undergoes a second fermentation in the presence of sour cherries before bottling results in kriek lambic, a beer closely related to gueuze.

Since gueuze is made by blending lambics, it tastes different from traditional ale and lager style beers. Because aged hops are used to produce these lambics, the beer has little to none of the traditional hop flavor and aroma that can be found in most other styles of beer. Furthermore, the wild yeasts that are specific to lambic-style beers give gueuze a dry, cider-like, musty, sour, acetic acid, lactic acid taste.