The kimono (着物; Japanese pronunciation: [kʲi.mo.no], lit. 'thing to wear') is a traditional Japanese garment and the national dress of Japan. The kimono is a wrapped-front garment with square sleeves and a rectangular body, and is worn left side wrapped over right, unless the wearer is deceased. The kimono is traditionally worn with a broad sash, called an obi, and is commonly worn with accessories such as zōri sandals and tabi socks.

Kimonos have a set method of construction and are typically made from a long, narrow bolt of cloth known as a tanmono, though Western-style fabric bolts are also sometimes used. There are different types of kimono for men, women, and children, varying based on the occasion, the season, the wearer's age, and – less commonly in the modern day – the wearer's marital status. Despite the kimono's reputation as a formal and difficult-to-wear garment, there are types of kimono suitable for both formal and informal occasions. The way a person wears their kimono is known as kitsuke (着付け, lit. 'dressing').

The history of the kimono can be tracked back to the Heian period (794–1185), when Japan's nobility embraced a distinctive style of clothing derived from Han China. Formerly the most common Japanese garment, the kimono has fallen out of favour and is rarely worn as everyday dress now. They are most often seen at summer festivals, where people frequently wear the yukata, the most informal type of kimono. More formal types are worn to funerals, weddings, graduations, and other formal events. Geisha and maiko are required to wear a kimono as part of their profession, and rikishi (sumo wrestlers) must wear kimonos at all times in public. Despite the small number of people who wear it regularly and its reputation as a complicated garment, the kimono has experienced revivals in previous decades, and is still worn today as fashionable clothing in Japan.

Before the Kofun period, reliable sources are scarce, so judgments are mainly based on the shapes of excavated artifacts such as haniwa. From these, we can already see garments of the kosode type, such as tsutsusode and tari-eri, as well as clothing considered to be prototypes of hakama.

The Nara period is considered a time when the upper classes were strongly influenced by China’s Tang dynasty, and many garments show the influence of Tang Hanfu. In addition, under the clothing regulations of the court, formal dress, court dress, and uniforms were prescribed. Meanwhile, the commoner classes wore simple and practical clothing, continuing to use ancient styles of upper garments and hakama even after this period.

In the early Heian period, the missions to Tang China were abolished and the Tang dynasty fell; from the mid to late Heian period onward, the so-called “national style culture” flourished. Among the upper classes, new garments such as the jūnihitoe and sokutai were created. These often consisted of wearing hakama on the lower body and layering multiple garments on the upper body in luxurious fashion. Within this aristocratic class, the kosode was worn simply as an undergarment for the upper body. On the other hand, among the common classes in the Heian and Kamakura periods, the kosode was everyday wear, combined with hakama or worn in a simplified upper garment-and-hakama style. Among the commoners, kosode were further simplified, often worn alone with only a waist sash. This is called kosode no kinagashi (wearing a kosode flowing). During this time, sleeves changed from cylindrical (tsutsusode) to narrow-cuffed (tsumesode). Examples include some women in the late Heian scroll painting Ban Dainagon Ekotoba and the women farming rice in Ōyamadera Engi. For the working classes, hakama could be a hindrance. Nevertheless, the kosode eventually became the foundation of the modern kimono.

From the latter half of the Kamakura period and into the Muromachi period, the weakening of the court nobility reached its peak. Moreover, as the samurai originally a military class close to commoners rose into the upper classes, the formerly extravagant upper garments disappeared. The kosode, which had been worn as the innermost garment, came to the forefront, merging with the kosode of the common people. Thus, in the Muromachi period, the simplest kosode, the prototype of the modern kimono, was born. The combination of kosode and hakama, called kosode-bakama, was treated as semi-formal attire in this period, later becoming formal wear. For example, the modern men’s formal attire haori-hakama consists of kosode and hakama with a haori coat over them. Eventually, even the upper classes dispensed with hakama, and the kosode worn flowing (kinagashi) became common informal wear regardless of class. Entering the Edo period, with the peace of the time, women’s kosode became more ornate, with greater variety of patterns and changes in shape according to demand. Sleeve length increased, and the obi grew longer and wider. To prevent the garment from loosening, the obijime cord originally used in Kabuki was adopted, leading to the modern furisode. During the Genroku era, kosode featured large sleeve pouches and flashy, innovative designs, while the hem was often worn long and trailing, with more relaxed dressing. Through these developments, the kosode evolved into what we recognize today as the modern kimono.

The first instances of kimono-like garments in Japan were traditional Chinese clothing introduced to Japan via Chinese envoys in the Kofun period (300–538 CE; the first part of the Yamato period), through immigration between the two countries and envoys to the Tang dynasty court leading to Chinese styles of dress, appearance, and culture becoming extremely popular in Japanese court society. The Imperial Japanese court quickly adopted Chinese styles of dress and clothing, with evidence of the oldest samples of shibori tie-dyed fabric stored at the Shōsōin Temple being of Chinese origin, due to the limitations of Japan's ability to produce the fabrics at the time. As early as the 4th century CE, images of priestess-queens and tribal chiefs in Japan depicted figures wearing clothing similar to that of Han dynasty China.