The parsnip (Pastinaca sativa) is a root vegetable closely related to carrot and parsley, all belonging to the flowering plant family Apiaceae. It is a biennial plant usually grown as an annual. Its long taproot has cream-colored skin and flesh, and, left in the ground to mature, becomes sweeter in flavor after winter frosts. In its first growing season, the plant has a rosette of pinnate, mid-green leaves. If unharvested, it produces a flowering stem topped by an umbel of small yellow flowers in its second growing season, later producing pale brown, flat, winged seeds. By this time, the stem has become woody, and the taproot inedible. Precautions should be taken when handling the stems and foliage, as parsnip sap can cause a skin rash or even blindness if exposed to sunlight after handling.

The parsnip is native to Eurasia; it has been used as a vegetable since antiquity and was cultivated by the Romans, although some confusion exists between parsnips and carrots in the literature of the time. It was used as a sweetener before the arrival of cane sugar in Europe.

Parsnips are usually cooked but can also be eaten raw. The flesh has a sweet flavor, even more so than carrots. It is high in vitamins, antioxidants, and minerals (especially potassium); and also contains both soluble and insoluble dietary fiber. Parsnips are best cultivated in deep, stone-free soil. The plant is attacked by the carrot fly and other insect pests, as well as viruses and fungal diseases, of which canker is the most serious.

The parsnip is a biennial plant with a rosette of roughly hairy leaves that have a pungent odor when crushed. Parsnips are grown for their fleshy, edible, cream-colored taproots. The roots are generally smooth, although lateral roots sometimes form. Most are narrowly conical, but some cultivars have a more bulbous shape, which generally tends to be favored by food processors as it is more resistant to breakage. The plant's apical meristem produces a rosette of pinnate leaves, each with several pairs of leaflets with toothed margins. The lower leaves have short stems, the upper ones are stemless, and the terminal leaves have three lobes. The leaves are once- or twice-pinnate with broad, ovate, sometimes lobed leaflets with toothed margins; they grow up to 40 centimetres (16 inches) long. The petioles are grooved and have sheathed bases. The floral stem develops in the second year and can grow to more than 150 cm (60 in) tall. It is hairy, grooved, hollow (except at the nodes), and sparsely branched. It has a few stalkless, single-lobed leaves measuring 5 to 10 cm (2 to 4 in) long that are arranged in opposite pairs.

The yellow flowers are in a loose, compound umbel measuring 10 to 20 cm (4 to 8 in) in diameter. Six to 25 straight pedicels are present, each measuring 2 to 5 cm (1 to 2 in) that support the umbellets (secondary umbels). The umbels and umbellets usually have no upper or lower bracts. The flowers have tiny sepals or lack them entirely, and measure about 3.5 millimetres (1⁄8 in). They consist of five yellow petals that are curled inward, five stamens, and one pistil. The fruits, or schizocarps, are oval and flat, with narrow wings and short, spreading styles. They are colored straw to light brown, and measure 4 to 8 mm (3⁄16 to 5⁄16 in) long.

Despite the slight morphological differences between the two, wild parsnip is the same taxon as the cultivated version, and the two readily cross-pollinate. The parsnip has a chromosome number of 2n=22.

Pastinaca sativa was first officially described by Carolus Linnaeus in his 1753 work Species Plantarum. It has acquired several synonyms in its taxonomic history:

Several species from other genera (Anethum, Elaphoboscum, Peucedanum, Selinum) are likewise synonymous with the name Pastinaca sativa.