A sandwich cookie (US and Canada), also known as a sandwich biscuit (UK, Ireland, Australia, New Zealand, and South Africa), is a type of cookie made from two cookies with a filling between them. Typically the hard, thin cookies known as biscuits outside North America are used, though some sandwich cookies use softer or thicker cookies. Many types of fillings are used, such as cream, ganache, buttercream, chocolate, cream cheese, jam, peanut butter, lemon curd, or ice cream.

Though they can be homemade, sandwich cookies are typically mass-produced and sold commercially. The sandwich biscuit market in Europe alone is worth over €1.6 billion a year, with Germany a consistently large consumer. Round sandwich biscuit varieties are more popular throughout Europe than squares, while the square varieties are more popular in Southern Europe than in the rest of the continent.^{[failed verification]}