Quinoa is a flowering plant in the amaranth family. It is a herbaceous annual plant grown as a crop primarily for its edible seeds; the seeds are rich in protein, dietary fiber, B vitamins, and dietary minerals in amounts greater than in many grains. Quinoa is not a grass, but rather a pseudocereal botanically related to spinach and amaranth (Amaranthus spp.), and originated in the Andean region of northwestern South America. It was first used to feed livestock 5,200–7,000 years ago, and for human consumption 3,000–4,000 years ago in the Lake Titicaca basin of Peru and Bolivia.

The plant thrives at high altitudes and produce seeds that are rich in protein. Almost all production in the Andean region is done by small farms and associations. Its cultivation has spread to more than 70 countries, including Kenya, India, the United States, and in European countries. As a result of increased popularity and consumption in North America, Europe, and Australasia, quinoa crop prices tripled between 2006 and 2014.

Chenopodium quinoa is a dicotyledonous annual plant, usually about 1–2 m (3–7 ft) high. It has broad, generally powdery, hairy, lobed leaves, normally arranged alternately. The woody central stem is branched or unbranched depending on the variety and may be green, red or purple. The flowering panicles arise from the top of the plant or from leaf axils along the stem. Each panicle has a central axis from which a secondary axis emerges either with flowers (amaranthiform) or bearing a tertiary axis carrying the flowers (glomeruliform). These are small, incomplete, sessile flowers of the same colour as the sepals, and both pistillate and perfect forms occur. Pistillate flowers are generally located at the proximal end of the glomeruli and the perfect ones at the distal end of it. A perfect flower has five sepals, five anthers and a superior ovary, from which two to three stigmatic branches emerge.

The plant's growth is highly variable due to the number of different subspecies, varieties and landraces (domesticated plants or animals adapted to the environment in which they originated). However, it is generally undemanding and altitude-hardy; it is grown from coastal regions to over 4,000 m (13,000 ft) in the Andes near the equator, with most of the cultivars being grown between 2,500 m (8,200 ft) and 4,000 m (13,000 ft). Depending on the variety, optimal growing conditions are in cool climates with temperatures that vary between −4 °C (25 °F) during the night to near 35 °C (95 °F) during the day. Some cultivars can withstand lower temperatures without damage. Light frosts normally do not affect the plants at any stage of development, except during flowering.