Intertextuality is the shaping of a text's meaning by another text, either through deliberate compositional strategies such as quotation, allusion, calque, plagiarism, translation, pastiche or parody, or by interconnections between similar or related works perceived by an audience or reader of the text. These references are sometimes made deliberately and depend on a reader's prior knowledge and understanding of the referent, but the effect of intertextuality is not always intentional and is sometimes inadvertent. Often associated with strategies employed by writers working in imaginative registers (fiction, poetry, and drama and even non-written texts like performance art and digital media), intertextuality may now be understood as intrinsic to any text.

Intertextuality has been differentiated into referential and typological categories. Referential intertextuality refers to the use of fragments in texts and the typological intertextuality refers to the use of pattern and structure in typical texts. A distinction can also be made between iterability and presupposition. Iterability makes reference to the "repeatability" of certain text that is composed of "traces", pieces of other texts that help constitute its meaning. Presupposition makes a reference to assumptions a text makes about its readers and its context. As philosopher William Irwin wrote, the term "has come to have almost as many meanings as users, from those faithful to Julia Kristeva's original vision to those who simply use it as a stylish way of talking about allusion and influence".

Julia Kristeva coined the term "intertextuality" (intertextualité) in an attempt to synthesize Ferdinand de Saussure's semiotics: his study of how signs derive their meaning from the structure of a text (Bakhtin's dialogism); his theory suggests a continual dialogue with other works of literature and other authors; and his examination of the multiple meanings, or "heteroglossia", of texts (especially novels) or individual words. According to Kristeva, "the notion of intertextuality replaces the notion of intersubjectivity" when we realize that meaning is not transferred directly from writer to reader but is instead mediated or filtered by "codes" imparted to the writer and reader by other texts. For example, when we read James Joyce's Ulysses we decode it as a modernist literary experiment or as a response to the epic tradition, or as part of some other conversation, or as part of many conversations at once. This intertextual view of literature, as shown by Roland Barthes, supports the concept that the meaning of a text does not reside in the text, but is produced by the reader in relation both to the text in question and the complex network of texts evoked by the reading process.

While the theoretical concept of intertextuality is associated with post-modernism, the device itself is not new. New Testament passages quote from the Old Testament and Old Testament books such as Deuteronomy or the prophets refer to the events described in Exodus (for discussions on using 'intertextuality' to describe the use of the Old Testament in the New Testament, see Porter 1997; Oropeza 2013; Oropeza & Moyise, 2016).^{[citation needed]} Whereas a redaction critic would use such intertextuality to argue for a particular order and process of the authorship of the books in question, literary criticism takes a synchronic view that deals with the texts in their final form, as an interconnected body of literature. This interconnected body extends to later poems and paintings that refer to Biblical narratives, just as other texts build networks around Greek and Roman Classical history and mythology.

More recent post-structuralist theory, such as that formulated in Daniela Caselli's Beckett's Dantes: Intertextuality in the Fiction and Criticism (MUP 2005), re-examines "intertextuality" as a production within texts, rather than as a series of relationships between different texts. Some postmodern theorists like to talk about the relationship between "intertextuality" and "hypertextuality" (not to be confused with hypertext, another semiotic term coined by Gérard Genette); intertextuality makes each text a "living hell of hell on earth" and part of a larger mosaic of texts, just as each hypertext can be a web of links and part of the whole World-Wide Web. The World-Wide Web has been theorized as a unique realm of reciprocal intertextuality, in which no particular text can claim centrality, yet the Web text eventually produces an image of a community—the group of people who write and read the text using specific discursive strategies.

Some examples of intertextuality in literature include:

Linguist Norman Fairclough states that "intertextuality is a matter of recontextualization". According to Per Linell, recontextualization can be defined as the "dynamic transfer-and-transformation of something from one discourse/text-in-context ... to another". Recontextualization can be relatively explicit—for example, when one text directly quotes another—or relatively implicit—as when the "same" generic meaning is rearticulated across different texts.

A number of scholars have observed that recontextualization can have important ideological and political consequences. For instance, Adam Hodges has studied how White House officials recontextualized and altered a military general's comments for political purposes, highlighting favorable aspects of the general's utterances while downplaying the damaging aspects. Rhetorical scholar Jeanne Fahnestock has found that when popular magazines recontextualize scientific research they enhance the uniqueness of the scientific findings and confer greater certainty on the reported facts. Similarly, John Oddo stated that American reporters covering Colin Powell's 2003 U.N. speech transformed Powell's discourse as they recontextualized it, bestowing Powell's allegations with greater certainty and warrantability and even adding new evidence to support Powell's claims.