Textual criticism is a branch of textual scholarship, philology, and literary criticism that is concerned with the identification of textual variants, or different versions, of either manuscripts (mss) or of printed books. Such texts may range in dates from the earliest writing in cuneiform, impressed on clay, for example, to multiple unpublished versions of a 21st-century author's work. Historically, scribes who were paid to copy documents may have been literate, but many were simply copyists, mimicking the shapes of letters without necessarily understanding what they meant.^{[citation needed]} This means that unintentional alterations were common when copying manuscripts by hand. Intentional alterations may have been made as well, for example, the censoring of printed work for political, religious or cultural reasons.

The objective of the textual critic's work is to provide a better understanding of the creation and historical transmission of the text and its variants. This understanding may lead to the production of a critical edition containing a scholarly curated text. If a scholar has several versions of a manuscript but no known original, then established methods of textual criticism can be used to seek to reconstruct the original text as closely as possible. The same methods can be used to reconstruct intermediate versions, or recensions, of a document's transcription history, depending on the number and quality of the text available.

On the other hand, the one original text that a scholar theorizes to exist is referred to as the urtext (in the context of Biblical studies), archetype or autograph; however, there is not necessarily a single original text for every group of texts. For example, if a story was spread by oral tradition, and then later written down by different people in different locations, the versions can vary greatly.

There are many approaches or methods to the practice of textual criticism, notably eclecticism, stemmatics, and copy-text editing. Quantitative techniques are also used to determine the relationships between witnesses to a text, called textual witnesses, with methods from evolutionary biology (phylogenetics) appearing to be effective on a range of traditions.

In some domains, such as religious and classical text editing, the phrase "lower criticism" refers to textual criticism and "higher criticism" to the endeavor to establish the authorship, date, and place of composition of the original text.

Textual criticism has been practiced for over two thousand years, as one of the philological arts. Early textual critics, especially the librarians of Hellenistic Alexandria in the last two centuries BC, were concerned with preserving the works of antiquity, and this continued through the Middle Ages into the early modern period and the invention of the printing press. Textual criticism was an important aspect of the work of many Renaissance humanists, such as Desiderius Erasmus, who edited the Greek New Testament, creating what developed as the Textus Receptus. In Italy, scholars such as Petrarch and Poggio Bracciolini collected and edited many Latin manuscripts, while a new spirit of critical enquiry was boosted by the attention to textual states, for example in the work of Lorenzo Valla on the purported Donation of Constantine.^{[citation needed]}

Many ancient works, such as the Bible and the Greek tragedies, survive in hundreds of copies, and the relationship of each copy to the original may be unclear. Textual scholars have debated for centuries which sources are most closely derived from the original, hence which readings in those sources are correct.^{[citation needed]} Although texts such as Greek plays presumably had one original, the question of whether some biblical books, like the Gospels, ever had just one original has been discussed.^{[page needed]} Interest in applying textual criticism to the Quran has also developed after the discovery of the Sana'a manuscripts in 1972, which possibly date back to the seventh to eighth centuries.^{[citation needed]}

In the English language, the works of William Shakespeare have been a particularly fertile ground for textual criticism—both because the texts, as transmitted, contain a considerable amount of variation, and because the effort and expense of producing superior editions of his works have always been widely viewed as worthwhile. The principles of textual criticism, although originally developed and refined for works of antiquity and the Bible, and, for Anglo-American Copy-Text editing, Shakespeare, have been applied to many works, from (near-)contemporary texts to the earliest known written documents. Ranging from ancient Mesopotamia and Egypt to the twentieth century, textual criticism covers a period of about five millennia.^{[citation needed]}