What fruit is the main ingredient in apple pie?

The main ingredient in apple pie is apples.

An apple pie is defined by its principal filling: apples enclosed in pastry. The fruit may be sliced, chopped, layered, or cooked into a softer filling before baking. Sugar, butter, flour or cornstarch, lemon juice, and spices help shape the flavor and texture, but they support the apples rather than replace them.

Different apple varieties create noticeably different pies. Tart, firm apples such as Granny Smith, Bramley, Cortland, and Northern Spy hold their shape and balance the sweetness of the crust. Some recipes blend several varieties to combine acidity, fragrance, and tenderness. Apples may also be fresh, canned, or reconstituted from dried fruit.

Apple pie has a long history outside the United States. Recipes existed in England by the 14th century, and related traditions developed across Europe, including Dutch lattice pies and French upside-down tarts such as tarte Tatin. The American association is powerful, but the dessert is an international apple-based tradition.