Nepeta cataria, commonly known as catnip and catmint, is a species of the genus Nepeta in the mint family, native to southern and eastern Europe, northern parts of the Middle East, and Central Asia. It is widely naturalized in northern Europe, New Zealand, and North America. The common name catmint can also refer to the genus as a whole.

It is a short-lived perennial mint-family herb growing 30–100 cm (12–39 in) tall with square stems, grayish canescent leaves that vary in shape and have serrated edges, fragrant small bilabiate flowers arranged in raceme spikes, and produces small three-sided nutlets containing one to four seeds. It was described by Carl Linnaeus in 1753, with no subspecies but multiple botanical synonyms, and its name—derived from medieval Latin—reflects its historical association with cats and various traditional names dating back to medieval England.

Catnip is named for the intense attraction about two-thirds of cats have to the plant due to the terpene nepetalactone, which acts as a natural insect repellent and induces playful, euphoric behavior in cats. It is used in herbal teas for its sedative and relaxant properties; it is drought-tolerant and deer-resistant.

Nepeta cataria is a short-lived perennial that grows 30 to 100 cm (12 to 39 in) tall, usually with several stems. Each of its stems is square in cross section, as typical of the mint family, and somewhat gray in color. It is a herbaceous plant that regrows from a taproot. It does not root deeply. Older plants tend to have more branches with particularly healthy plants becoming mound shaped.

The leaves are canescent in appearance, white in color due to being covered in fine hairs, especially so on the lower side of the leaves. They are attached in pairs to opposite sides of the stems. Leaf shapes vary from cordate, deltoid, to ovate; shaped like a heart, triangle, or like an egg. They are attached by leaf stems and have a length of 2 to 9 cm (0.8 to 3.5 in) and 0.6 to 6 cm (0.2 to 2.4 in) wide. The edges of the leaves are coarsely crenate to serrate, having a wavy, rounded edge to have asymmetrical teeth like those of a saw that point forward.

The flowers are in loose groups in an inflorescence. The lowest flowers are more widely spaced and at the end more tightly packed into a spike. The inflorescences lie at the end of the branches and may be 2 to 8 cm (0.8 to 3.1 in) long, with inconspicuous bracts. A single plant may produce several thousand flowers, but at any given time, less than 10% of them will be in full bloom. The flowers themselves are somewhat small and inconspicuous, but quite fragrant. They are bilaterally symmetrical and measure 10 to 12 mm (0.39 to 0.47 in) long. The petals are off-white to pink and usually dotted with purple-pink spots. They are bilabiate with the upper lip having two lobes and the lower one much wider with a scalloped edge.

The fruit is a nutlet that is nearly triquetrous, three sided with sharp edges and concave sides, and overall shaped like an egg. They measure approximately 1.7 by 1 mm (0.067 by 0.039 in). Each nutlet may contain between one and four seeds. They are dark reddish-brown in color with two white spots near the base.

Nepeta cataria was one of the many species described by Linnaeus in 1753 in his landmark work Species Plantarum. He had previously described it in 1738 as Nepeta floribus interrupte spicatis pedunculatis (meaning "Nepeta with flowers in a stalked, interrupted spike"), before the commencement of Linnaean taxonomy. Catnip is classified in part of Nepeta in the Lamiaceae, commonly known as the mint family. It has no subspecies or varieties.