Bonsai (/ˈbɒnsaɪ/; Japanese: 盆栽, lit. 'tray planting', pronounced [boɰ̃sai] ⓘ)[1] is the Japanese art of growing and shaping miniature trees in containers, developed from the traditional Chinese art form of penjing (盆景). Penjing and bonsai differ in that the former attempts to display "wilder," more naturalistic scenes, often representing landscapes, including elements such as water, rocks, or figurines; on the other hand, bonsai typically focuses on a single tree or a group of trees of the same species, with a higher level of aesthetic refinement.[2][3] Similar versions of the art exist in other cultures, including the miniature living landscapes of Vietnamese Hòn non bộ. During the Tang dynasty, when penjing was at its height, the art was first introduced from China.

The loanword "bonsai" has become an umbrella term in English, attached to many forms of diminutive potted plants,[4] and also on occasion to other living and non-living things. According to Stephen Orr in The New York Times, "the term should be reserved for plants that are grown in shallow containers following the precise tenets of bonsai pruning and training, resulting in an artful miniature replica of a full-grown tree in nature."[5] In the most restrictive sense, "bonsai" refers to miniaturized, container-grown trees adhering to Japanese tradition and principles.

Purposes of bonsai are primarily contemplation for the viewer, and the pleasant exercise of effort and ingenuity for the grower.[6] In contrast to other plant cultivation practices, bonsai are not grown for the production of food or for medicine.

A bonsai is created beginning with a specimen of source material. This may be a cutting, seedling, a tree from the wild (known as Yamadori) or small tree of a species suitable for bonsai development. Bonsai can be created from nearly any perennial woody-stemmed tree or shrub species[7] that produces true branches and can be cultivated to remain small through pot confinement with crown and root pruning. Some species are popular as bonsai material because they have characteristics, such as small leaves or needles, that make them appropriate for the compact visual scope of bonsai.