Jujutsu (Japanese: 柔術 jūjutsu, Japanese pronunciation: [dʑɯːʑɯtsɯ] or [dʑɯꜜːʑɯtsɯ] ^ⓘ), also known as Japanese jiu-jitsu and simply jiu-jitsu or ju-jitsu (both /dʒuːˈdʒɪtsuː/ joo-JITS-oo), is a Japanese martial art and a system of close combat that can be used in a defensive or offensive manner to kill or subdue one or more weaponless or armed and armored opponents. A subset of techniques from certain styles of jujutsu were used to develop many modern martial arts and combat sports, such as judo, aikido, sambo, Brazilian jiu-jitsu, ARB, and mixed martial arts.

"Jū" can be translated as "gentle, soft, supple, flexible, pliable, or yielding", and "jutsu" can be translated as "art or technique". "Jujutsu" thus has the meaning of "yielding-art", as its core philosophy is to manipulate the opponent's force against themself rather than confronting it with one's own force. Jujutsu developed to combat the samurai of feudal Japan as a method for defeating an armed and armored opponent in which one uses no form of weapon, or only a short weapon. Because striking against an armored opponent proved ineffective, practitioners learned that the most efficient methods for neutralizing an enemy took the form of pins, joint locks, and throws. These techniques were developed around the principle of using an attacker's energy against them, rather than directly opposing it.

There are many variations of the art, which leads to a diversity of approaches. Jujutsu schools (ryū) may utilize all forms of grappling techniques to some degree (e.g., throwing, takedowns, leg sweeps, trapping, pins, joint locks, holds, chokeholds, strangulation, gouging, biting, hair pulling, disengagements, and striking). In addition to jujutsu, many schools teach the use of weapons. Today, jujutsu is practiced in both traditional self-defense oriented and modern sports forms. Derived sport forms include the Olympic sport and martial art of judo, which was developed by Kanō Jigorō in the late 19th century from several traditional styles of jujutsu, and sambo and Brazilian jiu-jitsu, which were derived from judo.

Jujutsu is derived using the Hepburn romanization system. Before the first half of the 20th century, however, jiu-jitsu and ju-jitsu were preferred, even though the romanization of the second kanji as jitsu is not faithful to the standard Japanese pronunciation. It was a non-standardized spelling resulting from how English speakers heard the second short u in the word, which is pronounced /ɯ/ and therefore close to a short English i.^{[citation needed]} This may also be a reflection of the speech of Shitamachi that merges 'ju' into 'ji'. Since Japanese martial arts first became widely known of in the West in that time period, these earlier spellings are still common in many places. Ju-jitsu is still a common spelling in France, Canada, and the United Kingdom while jiu-jitsu is most widely used in Germany and Brazil. Different from the Japanese pronunciation, the word Jujutsu is still usually pronounced as if it is spelled jujitsu in the United States.

Some define jujutsu and similar arts rather narrowly as "unarmed" close combat systems used to defeat or control an enemy who is similarly unarmed. Basic methods of attack include hitting or striking, thrusting or punching, kicking, throwing, pinning or immobilizing, strangling, and joint locking. Great pains were also taken by the bushi (classic warriors) to develop effective methods of defense, including parrying or blocking strikes, thrusts and kicks, receiving throws or joint locking techniques (i.e., falling safely and knowing how to "blend" to neutralize a technique's effect), releasing oneself from an enemy's grasp, and changing or shifting one's position to evade or neutralize an attack. As jujutsu is a collective term, some schools or ryu adopted the principle of ju more than others.

From a broader point of view, based on the curricula of many of the classical Japanese arts themselves, however, these arts may perhaps be more accurately defined as unarmed methods of dealing with an enemy who was armed, together with methods of using minor weapons such as the jutte (truncheon; also called jitter), tantō (knife), or kakushi buki (hidden weapons), such as the ryofundo kusari (weighted chain) or the bankokuchoki (a type of knuckle-duster), to defeat both armed or unarmed opponents.

Furthermore, the term jujutsu was also sometimes used to refer to tactics for infighting used with the warrior's major weapons: katana or tachi (sword), yari (spear), naginata (glaive), jō (short staff), and bō (quarterstaff). These close combat methods were an important part of the different martial systems that were developed for use on the battlefield. They can be generally characterized as either Sengoku period (1467–1603) katchu bu Jutsu or yoroi kumiuchi (fighting with weapons or grappling while clad in armor), or Edo period (1603–1867) suhada bu Jutsu (fighting while dressed in the normal street clothing of the period, kimono and hakama).

The first Chinese character of jujutsu (Chinese and Japanese: 柔; pinyin: róu; rōmaji: jū; Korean: 유; romaja: yu) is the same as the first one in judo (Chinese and Japanese: 柔道; pinyin: róudào; rōmaji: jūdō; Korean: 유도; romaja: yudo). The second Chinese character of jujutsu (traditional Chinese and Japanese: 術; simplified Chinese: 术; pinyin: shù; rōmaji: jutsu; Korean: 술; romaja: sul) is the same as the second one in bujutsu (traditional Chinese and Japanese: 武術; simplified Chinese: 武术; pinyin: wǔshù; rōmaji: bujutsu; Korean: 무술; romaja: musul).