Solanaceae (/ˌsɒləˈneɪsi.iː, -ˌaɪ/), commonly known as the nightshades, is a family of flowering plants in the order Solanales. The family contains approximately 2,700 species, several of which are used as agricultural crops, medicinal plants, and ornamental plants. Many members of the family have high alkaloid contents, making some highly toxic, but many—such as tomatoes, potatoes, eggplants, and peppers—are commonly used in food.

Originating in South America, Solanaceae now inhabit every continent on Earth except Antarctica. After the K–Pg extinction event they rapidly diversified and have adapted to live in deserts, tundras, rainforests, plains, and highlands, and taken on wide range of forms including trees, vines, shrubs, and epiphytes. Nearly 80% of all nightshades are included in the subfamily Solanoideae, most of which are members of the type genus Solanum. Most taxonomists recognize six other subfamilies: Cestroideae, Goetzeoideae, Nicotianoideae, Petunioideae, Schizanthoideae, and Schwenkioideae, although nightshade taxonomy is still controversial. The genus Duckeodendron is sometimes placed in its own subfamily, Duckeodendroideae.

The high alkaloid content in some species has made them valuable for recreational, medicinal, and culinary use. The tobacco plant has been used for centuries as a recreational drug because of its high nicotine content. The tropanes in Atropa bella-donna can have pain-killing, relaxing, or psychedelic effects, making it a popular plant in alternative medicine, as well as one of the most toxic plants in the world. The presence of capsaicin in Capsicum species gives their fruits their signature pungency, which are used to make most spicy food products sold today. The potato, tomato, and eggplant, while not usually used for their alkaloids, also have an extensive presence in cuisine. Various food products like ketchup, potato chips, french fries, and multiple regional dishes are extremely commonly eaten around the world. Other nightshades are known for their beauty, such as the long, slender flowers of Brugmansia, the various colors of Petunia, or the spotted and speckled varietes of Schizanthus.

The name "Solanaceae" comes from Solanum, the type genus of the family, + -aceae, the suffix for plant family names. The etymology of the word solanum is unclear. The name probably comes from a perceived resemblance of certain species' flowers to the sun (sol in Latin) and its rays. At least one species of Solanum is known as the "sunberry". Alternatively, the name could originate from the Latin verb solare, meaning "to soothe", presumably referring to the soothing pharmacological properties of some of the psychoactive species of the family.

The common name "nightshade" developed directly from Middle English nyght-shade, originating from the Old English word nihtscada (lit. "shade of night"), cognate with Germanic words such as German nachtschatten and Dutch nachtschade. The reason for these names is unknown, but could have been a reference to the appearance of the fruits.

Nightshades can take the form of herbs, shrubs, trees, vines and lianas, and sometimes epiphytes. They can be annuals, biennials, or perennials, upright or decumbent. Some have subterranean tubers. They do not have laticifers, nor latex, nor coloured saps. They can have a basal or terminal group of leaves or neither of these types. The leaves are generally alternate or alternate to opposed (that is, alternate at the base of the plant and opposed towards the inflorescence). The leaves can be herbaceous, leathery, or transformed into spines. The leaves are generally petiolate or subsessile, rarely sessile. They are frequently inodorous, but some are aromatic or fetid. The foliar lamina can be either simple or compound, and the latter can be either pinnatifid or ternate. The leaves have reticulated venation and lack a basal meristem. The laminae are generally dorsiventral and lack secretory cavities. The stomata are generally confined to one of a leaf's two sides; they are rarely found on both sides.

The flowers are generally hermaphrodites, although some are monoecious, andromonoecious, or dioecious species (such as some Solanum or Symonanthus). They are most commonly pollinated by insects. The flowers can be solitary or grouped into terminal, cymose, or axillary inflorescences. The flowers are medium-sized, fragrant (Nicotiana), fetid (Anthocercis), or inodorous. The flowers are usually actinomorphic, slightly zygomorphic, or markedly zygomorphic (for example, in flowers with a bilabial corolla in Schizanthus species). The irregularities in symmetry can be due to the androecium, to the perianth, or both at the same time. In the great majority of species, the flowers have a differentiated perianth with a calyx and corolla (with five sepals and five petals, respectively) an androecium with five stamens and two carpels forming a gynoecium with a superior ovary (they are therefore referred to as pentamers and tetracyclic). The stamens are epipetalous and are typically present in multiples of four or five, most commonly four or eight. They usually have a hypogynous disk. The calyx is gamosepalous (as the sepals are joined forming a tube), with the (4)5(6) segments equal, it has five lobes, with the lobes shorter than the tube, it is persistent and often accrescent. The corolla usually has five petals that are also joined forming a tube. Flower shapes are typically rotate (wheel-shaped, spreading in one plane, with a short tube) or tubular (elongated cylindrical tube), campanulated, or funnel-shaped.

The androecium has (2)(4)5(6) free stamens within its opposite sepals (they alternate with the petals). They are usually fertile or, in some cases (for example in Salpiglossideae) they have staminodes. In the latter case, there is usually either one staminode (Salpiglossis) or three (Schizanthus). The anthers touch on their upper end forming a ring, or they are completely free, dorsifixed, or basifixed with poricide dehiscence or through small longitudinal cracks. The stamen's filament can be filiform or flat. The stamens can be inserted inside the coralline tube or exserted. The plants demonstrate simultaneous microsporogenesis, the microspores are tetrad, tetrahedral, or isobilateral. The pollen grains are bicellular at the moment of dehiscence, usually open and angular.