Unicode (also known as The Unicode Standard and TUS) is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 17.0 defines 159,801 characters and 172 scripts used in various ordinary, literary, academic, and technical contexts.

Unicode has largely supplanted the previous environment of myriad incompatible character sets used within different locales and on different computer architectures. The entire repertoire of these sets, plus many additional characters, were merged into the single Unicode set. Unicode is used to encode the vast majority of text on the Internet, including most web pages, and relevant Unicode support has become a common consideration in contemporary software development. Unicode is ultimately capable of encoding more than 1.1 million characters.

The Unicode character repertoire is synchronized with ISO/IEC 10646, each being code-for-code identical with one another. However, The Unicode Standard is more than just a repertoire within which characters are assigned. To aid developers and designers, the standard also provides charts and reference data, as well as annexes explaining concepts germane to various scripts, providing guidance for their implementation. Topics covered by these annexes include character normalization, character composition and decomposition, collation, and directionality.

Unicode encodes 3,790 emoji, with the continued development thereof conducted by the Consortium as a part of the standard. The widespread adoption of Unicode was in large part responsible for the initial popularization of emoji outside of Japan.^{[citation needed]}

Unicode text is processed and stored as binary data using one of several encodings, which define how to translate the standard's abstracted codes for characters into sequences of bytes. The Unicode Standard itself defines three encodings: UTF-8, UTF-16, and UTF-32, though several others exist. UTF-8 is the most widely used by a large margin, in part due to its backwards-compatibility with ASCII.

Unicode was originally designed with the intent of transcending limitations present in all text encodings designed up to that point: each encoding was relied upon for use in its own context, but with no particular expectation of compatibility with any other. Indeed, any two encodings chosen were often totally unworkable when used together, with text encoded in one interpreted as garbage characters by the other. Most encodings had only been designed to facilitate interoperation between a handful of scripts—often primarily between a given script and Latin characters—not between a large number of scripts, and not with all of the scripts supported being treated in a consistent manner.

The philosophy that underpins Unicode seeks to encode the underlying characters—graphemes and grapheme-like units—rather than graphical distinctions considered mere variant glyphs thereof, that are instead best handled by the typeface, through the use of markup, or by some other means. In particularly complex cases, such as the treatment of orthographical variants in Han characters, there is considerable disagreement regarding which differences justify their own encodings, and which are only graphical variants of other characters.

At the most abstract level, Unicode assigns a unique number called a code point to each character. Many issues of visual representation—including size, shape, and style—are intended to be up to the discretion of the software actually rendering the text, such as a web browser or word processor. However, partially with the intent of encouraging rapid adoption, the simplicity of this original model has become somewhat more elaborate over time, and various pragmatic concessions have been made over the course of the standard's development.