Mojibake (文字化け^?) (IPA: [modʑibake]; lit. "character transformation"), from the Japanese 文字 (moji) "character" + 化け (bake) "transform", is the occurrence of incorrect, unreadable characters shown when software fails to render text correctly according to its associated character encoding.

Mojibake is often caused when a character encoding is not correctly tagged in a document, or when a document is moved to a system with a different default encoding. Such incorrect display occurs when writing systems or character encodings are mistagged or "foreign" to the user's computer system: if a computer does not have the software required to process a foreign language's characters, it will attempt to process them in its default language encoding, usually resulting in gibberish. Messages transferred between different encodings of the same language can also have mojibake problems. Japanese language users, with several different encodings historically employed, encounter this problem relatively often. For example, the intended word "文字化け", encoded in UTF-8, is incorrectly displayed as "æ–‡å—化け" in software that is configured to expect text in the Windows-1252 or ISO-8859-1 encodings, usually labelled Western.