Fennel (Foeniculum vulgare) is the most important species in the genus Foeniculum (treated as the sole species by many botanists), and is native to southern Europe (especially by the Mediterranean) and southwestern Asia.

It is a highly aromatic perennial herb, erect, glaucous green, and grows to 2 m tall. The leaves grow up to 40 cm long; they are finely dissected, with the ultimate segments filiform, about 0.5 mm wide. The flowers are produced in terminal compound umbels 5-15 cm wide, each umbel section with 20-50 tiny yellow flowers on short pedicels. The fruit is a dry seed from 4-9 mm long, half as wide or less, and grooved.

The Florence fennel (Cultivar Group F. vulgare Azoricum Group) is a selection with inflated leaf bases which form a sort of bulb. It comes mainly from India and Egypt and it has a mild anise-like flavour, but is more aromatic and sweeter. Its flavour comes from anethole, an aromatic compound also found in anise and star anise. Florence fennel is smaller than the wild type and has inflated leaf bases which are eaten as a vegetable, both raw and cooked. There are several cultivars of Florence fennel, which is also known by several other names, notably the Italian name finocchio.

Fennel has become naturalised along roadsides, in pastures, and other open sites in many regions, including northern Europe, the United States, southern Canada and in much of Asia and Australia. It is propagated by seed, and is considered to be a weed in Australia and the United States.