Ideophones are words that vividly depict sensory experience with marked forms. They abound in many languages of the world, including Niger-Congo, Afro-Asiatic, Dravidian, Austroasiatic, and Quechuan languages as well as Japanese, Korean, Turkish, and Basque. The term “ideophone” originates in Bantu linguistics but is applied across languages. Ideophones are also known as “mimetics” in Japanese linguistics and “expressives” in South and Southeast Asian linguistics. Arguably all spoken languages have onomatopoeic (sound-imitative) ideophones (e.g., woof-woof, wham), and many languages also have ideophones for non-auditory information, such as motion (e.g., plisti-plasta ‘walking in water’ (Basque)), shine (e.g., ɡéɡéréré ‘shining brightly’ (Chewa)), shape (e.g., tíɡhí-tìɡhì-tíɡhí ‘twisted’ (Edo)), and texture (e.g., lip rip ‘smooth, flat’ (Hausa)). Ideophones in some languages further depict color (e.g., yibɔɔ ‘black’ (Ewe)), taste and smell (e.g., thuu ‘smelling horribly’ (Venda)), proprioceptive sensations (e.g., rupax ‘intensely warm or burning’ (Pastaza Quichua)), and emotion (e.g., zokuzoku ‘thrilled’ (Japanese)). These sensory meanings are often iconically represented by some marked morphophonological features, such as unusual phonotactics (e.g., /ɡb/ (Kisi)), vowel or tonal harmony (e.g., ɡbànɡbàlànɡ ‘long pole falling down’ (Dagaare)), and total or partial reduplication (e.g., tʃoɭtʃoɭ ‘in continuous flow’ (Korean), kananaa ‘silent’ (Siwu)). The formal markedness of ideophones may be further emphasized by lengthening (e.g., baaaang), prominent intonation, special phonation (e.g., falsetto, creaky voice), distinct speech rate, and syntactic isolation (e.g., holophrastic realization). Moreover, as a nonverbal manifestation of their performative nature, ideophones often synchronize with iconic gestures. Ideophones constitute a prototype category for which none of these features are either necessary or sufficient, and often, one cannot decide clearly whether a word is an ideophone or not. Furthermore, ideophones are integrated with the linguistic system to varying degrees both within and across languages. For example, holophrastic ideophones tend to have expressive prosody and be accompanied by iconic gestures, whereas predicative ideophones tend to be plain. Reflecting this behavioral diversity of ideophones, earlier studies focused on sound-symbolic generalizations and categorial definitions in individual languages, notably Asian and African languages. However, a growing body of research from the 1990s onward has sought the theoretical and typological significance of this word class.