Semiotics is the study of signs. It is an interdisciplinary field that examines what signs are, how they form sign systems, and how individuals use them to communicate meaning. Its main branches are syntactics, which addresses formal relations between signs, semantics, which addresses the relation between signs and their meanings, and pragmatics, which addresses the relation between signs and their users. Semiotics is related to linguistics but has a broader scope that includes nonlinguistic signs, such as maps and clothing.

Signs are entities that stand for something else, like the word cat, which stands for a carnivorous mammal. They can take many forms, such as sounds, images, written marks, and gestures. Iconic signs operate through similarity. For them, the sign vehicle resembles the referent, such as a portrait of a person. Indexical signs are based on a direct physical link, such as smoke as a sign of fire. For symbolic signs, the relation between sign vehicle and referent is conventional or arbitrary, which applies to most linguistic signs. Models of signs analyze the basic components of signs. Ferdinand de Saussure's dyadic model identifies a perceptible image and a concept as the core elements, whereas Charles Sanders Peirce's triadic model distinguishes a sign vehicle, a referent, and an effect in the interpreter's mind.

Sign systems are structured networks of interrelated signs, such as the English language. Semioticians study how signs combine to form larger expressions, called texts. They explore how the message of a text depends on the meanings of the signs composing it and how contextual factors and tropes influence this process. They also investigate the codes employed to communicate meaning, including conventional codes, such as the color code of traffic signals, and natural codes, such as DNA encoding hereditary information.

Semiotics has diverse applications because of the pervasive nature of signs. Many semioticians study cultural products, such as literature, art, and media, investigating both the elements used to express meaning and the subtle ideological messages they convey. The psychological activities associated with sign use are another research topic. Biosemiotics extends the scope of inquiry beyond human communication, examining sign processes within and between animals, plants, and other organisms. Semioticians typically adjust their research approach to their specific domain without a single methodology adopted by all subfields. Although the roots of semiotic research lie in antiquity, it was not until the late 19th and early 20th centuries that semiotics emerged as an independent field of inquiry.

Semiotics is the study of signs or of how meaning is created and communicated through them. Also called semiology, it examines the nature of signs, their organization into signs systems, like language, and the ways individuals interpret and use them. Semiotics has wide-reaching applications because of the pervasive nature of signs, affecting how individuals experience phenomena, communicate ideas, and interact with the world.

These applications make it an interdisciplinary field, originating in philosophy and linguistics and closely related to disciplines like psychology, anthropology, aesthetics, sociology, and education sciences. Because most sciences rely on sign processes in some form, semiotics is sometimes characterized as a meta-discipline that provides a general approach for the analysis of signs across domains. It is controversial whether semiotics is itself a science since there are no universally accepted theoretical assumptions or methods on which semioticians agree. Semiotics has also been characterized as a theory, a doctrine, a movement, or a discipline. Apart from its interdisciplinary applications, pure semiotics is typically divided into three branches: semantics, syntactics, and pragmatics, studying how signs relate to objects, to each other, and to sign users, respectively.

Semiotic inquiry overlaps in various ways with linguistics and communication theory. It shares with linguistics the interest in the analysis of sign systems, examining the meanings of words, how they are combined to form sentences, and how they convey messages in concrete contexts. A key difference is that linguistics focuses on language, while semiotics also studies non-linguistic signs, such as images, gestures, traffic signs, and animal calls. Communication theory studies how individuals encode, convey, and interpret both linguistic and non-linguistic messages. It typically focuses on technical aspects of how messages are transmitted, usually between distinct organisms. Semiotics, by contrast, concentrates on the meaning of messages and the creation of meaning, including the role of non-communicative signs. For example, semioticians also study naturally occurring biological signs, like disease symptoms, and signs based on inanimate relations, such as smoke as a sign of fire.

The term semiotics derives from the Greek word σημειωτική (semeiotike), originally associated with the study of disease symptoms. Proposing a new field of inquiry of signs, John Locke suggested the Greek term as its name. The first use of the English term semiotics dates to the 1670s. Semiotics became a distinct field of inquiry following the works of the philosopher Charles Sanders Peirce and the linguist Ferdinand de Saussure, the founders of the discipline.