The zucchini ( (listen); plural: zucchini or zucchinis), courgette (; plural: courgettes) or baby marrow (Cucurbita pepo) is a summer squash, a vining herbaceous plant whose fruit are harvested when their immature seeds and epicarp (rind) are still soft and edible. It is closely related, but not identical, to the marrow; its fruit may be called marrow when mature.

Ordinary zucchini fruit are any shade of green, though the golden zucchini is a deep yellow or orange. At maturity, they can grow to nearly 1 metre (3 feet) in length, but they are normally harvested at about 15–25 cm (6–10 in).

In botany, the zucchini's fruit is a pepo, a berry (the swollen ovary of the zucchini flower) with a hardened epicarp. In cookery, it is treated as a vegetable, usually cooked and eaten as an accompaniment or savory dish, though occasionally used in sweeter cooking.

Zucchini occasionally contain toxic cucurbitacins, making them extremely bitter, and causing severe gastero-enteric upsets. Causes include stressed growing conditions, and cross pollination with ornamental squashes.

Zucchini descends from squashes first domesticated in Mesoamerica over 7,000 years ago, but the zucchini itself was bred in Milan in the late 19th century.