Writing is the act of creating a persistent representation of language. A writing system includes a particular set of symbols called a script, as well as the rules by which they encode a particular spoken language. Every written language arises from a corresponding spoken language; while the use of language is universal across human societies, most spoken languages are not written.

Writing is a cognitive and social activity involving neuropsychological and physical processes. The outcome of this activity, also called writing (or a text) is a series of physically inscribed, mechanically transferred, or digitally represented symbols. Reading is the corresponding process of interpreting a written text, with the interpreter referred to as a reader.

In general, writing systems do not constitute languages in and of themselves, but rather a means of encoding language such that it can be read by others across time and space. While not all languages use a writing system, those that do can complement and extend the capacities of spoken language by creating durable forms of language that can be transmitted across space (e.g. written correspondence) and stored over time (e.g. libraries). Writing can also impact what knowledge people acquire, since it allows humans to externalize their thinking in forms that are easier to reflect on, elaborate on, reconsider, and revise.

Any instance of writing involves a complex interaction among available tools, intentions, cultural customs, cognitive routines, genres, tacit and explicit knowledge, and the constraints and limitations of the systems used. Writing implements used to make physical inscriptions include fingers, styluses, ink brushes, pencils, pens, and many styles of lithography; writing surfaces on which inscriptions may be made include stone tablets, clay tablets, bamboo slips, papyrus, wax tablets, vellum, parchment, paper, copperplate, and slate.

The typewriter, as well as the digital word processor, allow individual writers to produce visually consistent text mechanically via a keyboard.

Advancements in natural language processing and natural language generation have resulted in software capable of producing certain forms of formulaic writing (e.g. weather forecasts and sports reporting) without the direct involvement of humans after initial configuration or, more commonly, to be used to support writing processes such as generating initial drafts, producing feedback with the help of a rubric, copy-editing, and helping translation.

Historically, writing emerged to address the needs of societies growing in economic and social complexity. Once developed, potential applications included tracking produce and other wealth, recording history, maintaining culture, codifying knowledge through curricula as well as lists of texts deemed to contain foundational knowledge (e.g. The Canon of Medicine) or artistic value (e.g. the literary canon). Aids to administration included legal codes, census records, contracts, deeds of ownership, taxation, trade agreements, and treaties. As Charles Bazerman explains, the "marking of signs on stones, clay, paper, and now digital memories—each more portable and rapidly traveling than the previous—provided means for increasingly coordinated and extended action as well as memory across larger groups of people over time and space." Further innovations included more uniform, predictable, and widely dispersed legal systems, the distribution of accessible versions of sacred texts, and furthering practices of scientific inquiry and knowledge management, all of which were largely reliant on portable and easily reproducible forms of inscribed language. The history of writing is co-extensive with uses of writing and the elaboration of activity systems that give rise to and circulate writing.

Individual motivations for writing include the ability to operate beyond the limitations of one's own memory (e.g. to-do lists, recipes, reminders, logbooks, maps, directions for complicated tasks or rituals), dissemination of ideas and coordination (e.g. essays, monographs, broadsides, plans, petitions, manifestos), creativity and storytelling, maintaining kinship and other social networks, business correspondence regarding goods and services, and life writing (e.g. a diary or journal).