M&M's (stylized as m&m's) are color-varied sugar-coated dragée chocolate confectionery, each of which has the letter "m" printed in lower case in white on one side, consisting of a candy shell surrounding a filling which varies depending upon the variety of M&M's. The original candy has a semi-sweet chocolate filling which, upon introduction of other variations, was branded as the "plain, normal" variety. Peanut M&M's, which feature a peanut coated in milk chocolate, and finally a candy shell, were the first variation to be introduced, and they remain a regular variety. Numerous other variations have been introduced, some of which are regular widespread varieties (peanut butter, almond, pretzel, crispy, dark chocolate, and caramel) while others are limited in duration or geographic availability. M&M's are the flagship product of the Mars Wrigley Confectionery division of Mars, Incorporated.

The candy originated in the United States in 1941, and M&M's have been sold in over 100 countries since 2003. They are produced in different colors, some of which have changed over the years. The candy-coated chocolate concept was copied by Forrest Mars Sr. from Smarties, which he had encountered during the Spanish Civil War (1936–1939). The sugar coating made it possible to carry chocolate in warm climates without it melting. The company's longest-lasting slogan reflects this: "the milk chocolate that melts in your mouth, not in your hand."

A traditional milk chocolate M&M weighs about 0.91 grams / 0.032 ounces and has about 4.7 calories (kcal) of food energy (1.7 kcal from fat). Despite common belief, each colored M&M does not have a different flavor and all possess the same chocolate taste.