The Zuozhuan 左传 "Commentary of Zuo" is a commentary and parallel version to the chronicle Chunqiu 春秋 "Spring and Autumn Annals". It is attributed to a certain Zuo Qiuming 左丘明. The Zuozhuan commentary as a very narrative text became so important for the interpretation and later use of the Chunqiu that it is commonly merged with the latter to the unit Chunqiu-Zuozhuan. It was, with even more stress on the commentary, called Zuoshi chunqiu 左氏春秋 "Spring and Autumn of Master Zuo".

Zuo Qiuming is said to have lived in the state of Lu in the early 6th century, as a contemporarian of Confucius, but somewhat younger than the great master. The Qing period scholar Zhu Yizun 朱彝尊 believed that Zuoqiu was a double-character family name. Yu Zhengxie 俞正燮 was of the opinion that his name was Qiu Ming 邱明 (丘明), while zuo was the designation of his office, namely "scribe to the left" (zuoshi 左史). History says the Zuo Qiuming wrote the Zuozhuan as a commentary in order to clarify obscure statements in the Chunqiu. The book must in fact have been compiled later, during the Warring States period 战国 (5th cent.-221 BC). The Tang period scholar Zhao Kuang 赵匡 was the first who doubted that "Master Zuo" was identical to Zuo Qiuming. The Qing period scholar Yao Nai 姚鼐 argued that the book must have been compiled by several persons, and assumed that one of the authors was the politician and military writer Wu Qi 吴起, or the Han period 汉 (206 BCE-220 CE) imperial librarian Liu Xin 刘歆. The date of compilation is unclear. The Qing scholar Cui Shu 崔述根 assumed that is was compiled in the late Warring States period. The Japanese scholar Kano Naoki 狩野直喜 argues that it must have been written during the time of Duke Xiao of Qin 秦孝公 (r. 362-338). Yang Bojun gives a time frame of between 403 and 389 BCE. From these dates it can be seen that Confucius' disciple Zuo Qiuming cannot have been the author of the Zuozhuan.

While the shortness of the Chunqiu text can be explained by the method to write down a few words as a kind of aide-mémoire for a history transmitted orally, the narrative text of the Zuozhuan dates from a time when historiographers exactly wrote down what happened and what acting persons said in particular situations. This kind of historiography can also be found in the histories Guoyu 国语 "Discourses of the States" and the Zhanguoce 战国策 "Stratagems of the Warring States", writing about history of the Spring and Autumn 春秋 (770 - 5th cent. BCE) and the Warring States period, respectively. In the concept of Confucian historiography the Chunqiu was seen as the warp threads (gang 纲), whereas the Zuozhuan represented the filling threads (mu 目). These "filling threads" were probably added by early Confucian disciples of the state of Wei 魏. For the compilation of the Zuozhuan they made use of other sources unknown in the state of Lu 鲁, where the Chunqiu chronicle had been written, namely parts of the Shangshu 尚书 "Book of Documents", as well as chronicles of other states, as the Zhouzhi 周志 "Records of [the royal house of] Zhou" or the Zhengshu 郑书 "The book of the state of Zheng". The Zuozhuan is extremely helpful to understand the short and often obscure entries of the Chunqiu. For example, there is an entry of the first year of Duke Yin 鲁隐公 (r. 722-712) providing not more information than that the Earl of Zheng defeated the ruler of the statelet of Duan 段 at a place called Yan (Zheng bo ke Duan yu Yan. 郑伯克段于鄢。). The Zuozhuan adds a more than 500 words long story of this event, describes the atrocious intrigue of the Earl of Zheng, the deceitful behaviour of Gong Shu Duan 共叔段, and the decisive role of consort Wu Jiang 武姜 in the affair that covered ten years before it evolved into a military campaign.

The detailed description of military activities is one of the strengths of the Zuozhuan. It narrates more than 400 campaigns and their pre-history, the movements of the battlefield, the tactics of the generals, and the results. Among these, some were of a high importance for the surviving of the feudal states, like the battle of Chengpu 城濮 in 632 between Jin 晋 and Chu 楚, the battle of Yao 殽 in 627 between Qin 秦 and Jin, the battle of Bi 邲 in 597 beween Jin and Chu, the battle of An 鞌 in 589 between Qi 齐 and Jin, or that of Yanling 鄢陵 in 575 between Jin and Chu. Interstate meetings and diplomatic envoys are likewise an important theme in the Zuozhuan. The right use of words in conversation (duici 对辞) was of greatest importance for diplomatic success, and such details can only be covered in a narrative type of history, like the Zuozhuan, and not in the concise statements of the Chunqiu. The Zuozhuan includes numerous examples how skilled diplomats contributed to the success of their missions. In many instances the author of the Zuozhuan includes his own critical commentary to historical events, and praised them as "proper" (li 礼) or as incorrect (fei li 非礼).

Duke Huan of Qi 齐桓公 (r. 685-643), for instance, is held in high esteem because he was able to restore order among the feudal states as the first hegemonial lord (ba 霸), yet on the other side, his moral conduct is criticized, as well as his political intrigues with Prince Chong'er 重耳 of Jin. Duke Ling of Jin 晋灵公 (r. 621-607) is rated as "not behaving like a lord" (bu jun 不君), Duke Ling of Chen 陈灵公 (r. 614-599) is harshly criticized for his audacity to wear sacrificial robes at the court, Duke Zhuang of Qi 齐庄公 (r. 554-548) for his indulgence in banquets and the improper conduct of his courtiers. Loyal and responsible courtiers are praised, like Yan Ying 晏婴, Shu Xiang 叔向, or the politician Zichan 子产. Political theories are also to be found, like in the statements of Ji Liang of Sui 随季梁, Sima Ziyu 司马子鱼 of Song 宋, Shi Kuang 师旷 of Jin, Han Xianzi 韩献子, Yan Ying, Shu Xiang, Yin Yi Sheng 阴饴甥, or Feng Hua 逢滑.

The Zuozhuan - often referred to as a "commentary" - is after all a different report of the same events as the Chunqiu Annals with a few significant differences. First, it covers a longer period than the Chunqiu, that is until 463 BCE (the Chunqiu only to 479), when the Earl of Zhi 知伯, a nobleman in the state of Jin, was killed. The Zuozhuan also gives an account of the birth of Duke Yin and of his accession to the throne of Lu. The second, even more noticeable, is the more narrative character of the Zuozhuan who makes a quite readable anecdote collection out of the dry, enigmatic Chunqiu classic. There are many events reported in the Zuozhuan that are not mentioned at all in the Chunqiu and vice versa, so one can barely say the Zuozhuan is a commentary to the old annals. The problem does not come up in Chinese where the word zhuan 传 "commentary" can also be read as chuan which means "tradition", "transmission". The title of Zuozhuan can thus also be interpreted as something like "the version of Zuo". The Zuozhuan broadly reports visits of the feudal lords to each other, state meetings and the conclusion of alliances, wars, hunting tours, the erection of city walls, marriages among the nobility, rebellions, murders, the history of individual noble houses and their extinction, and so gives a detailed overview of the social happenings and activities of the ruling class. Yet other social groups are also mentioned, especially merchants, diviners, assassins, musicians, consorts, craftsmen and slaves. It provides an overview of the rise and fall of the institution of hegemonial lord that was initiated by Duke Huan of Qi, brought into a mature state by Duke Wen of Jin 晋文公 (r. 636-628), and was then taken over by Duke Mu of Qin 秦穆公 (r. 659-621), and then the native kings Zhuang of Chu 楚庄王 (r. 613-591), He Lü of Wu 吴王阖闾 (r. 514-496 BCE) and Gou Jian of Yue 越王句践 (r. 495- 465). The Zuozhuan furthermore clearly describes how the ducal power in some of the feudal states fell into the hands of sidelines or noble families, like the Jisun 季孙 in Lu, Tian 田 in Qi, and the houses of Han 韩, Zhao 赵 and Wei 魏 in Jin. It gives insight into political reforms like those under Zichan in the state of Zheng 郑.
A lot of statements in the Zuozhuan show that the late Spring and Autumn period was an age in which the ancient belief in the influence of ghosts and demons was more and more replaced with a belief in the Five Processes (wuxing 五行). Aerolites (stony meteorites, yunshi 陨石), for instance, were by royal secretary (neishi 内史) Shu Xing 叔兴 explained as a matter of Yin and Yang 阴阳, and not as an inauspicious omina. Similarly, a physician in the state of Qin believed that illness was influenced by the "six (meteorological) energies (liuqi 六气)", and not by demons. Zi Shen 梓慎 and Shusun Zhaozi 叔孙昭子 from Lu explained that solar eclipses and inundations were the result of the agency of Yin and Yang. Shi Mo 史墨 from Jin explained that the earth possesses the Five Processes, Zihan 子罕 from Song said that Heaven produces the Five Agents (wucai 五材), and the famous politician Zichan from Zheng argued that the Heavenly Way is far away, while the Human Way (rendao 人道) was close by, and that nature cannot be appeased by offering gifts.

A kind of basic dialectic thought can be found in some statement of the philosopher Yan Ying who deliberated about similarities and contradictions, as well as mutual completion and mutual support. Shi Mo from Jin is quoted with a statement about the changing nature of rulership and even the impermanence of dynasties (symbolized in their offering rituals).

The Zuozhuan was often criticized for the illustrative, vivid and narrative style of its stories that stands in deep contrast to the short and dry statements in the Chunqiu. On the other side, this contrast demonstrates that the Zuozhuan has a high literary standing that goes far beyond the frame of historiography. Liu Zhiji 刘知几, the great Tang period critic of historiography, therefore praised the Zuozhuan for its important contribution, and the Qing period scholar Liu Xizai 刘熙载 even said that it was the best of all histories. It therefore served as a rich source for later histories and is abundantly quoted in Sima Qian's 司马迁 Shiji 史记 from the Han period and Sima Guang's 司马光 Zizhi tongjian 资治通鉴 from the Song period 宋 (960-1279).