Cider or cyder ( /ˈsaɪdər/ sy-dər) is a fermented alcoholic beverage made from apple juice. Cider varies in alcohol content from 2% abv to 8.5% abv or more in traditional English ciders. In some regions, such as Germany and America, cider may be termed "apple wine". In current usage of the term in the United States and Canada, the term "hard cider" is used for the alcoholic beverage discussed in this article, while the term "cider" usually refers to a non-alcoholic apple juice beverage. When sugar or extra fruit has been added and a secondary fermentation increases the alcoholic strength, a cider is classified as "apple wine" in the United States.

Cider may be made from any variety of apple, but certain cultivars grown solely for use in cider are known as cider apples. Cider is popular in the United Kingdom, especially in South West England and East Anglia. The United Kingdom has the highest per capita consumption of cider, as well as the largest cider-producing companies in the world, including H. P. Bulmer, the largest. As of 2006^[update], the UK produces 600 million litres of cider each year (130 million imperial gallons).