在自然语言和形式语言中，如果一句句子直接或间接提及自身，就称为自指。自指可以是直接的，比如说谎者悖论，也可以是通过另外一句句子间接提及自身，还可以是通过某种编码反应自身，自指的语句常常会造成悖论。

自指在数学、哲学、计算机科学、语言学中都有被研究。在数学中，对自指的研究最终导致了著名的哥德尔不完备定理。在哲学中，“自指”一词也指代主体谈论或提及自身的能力。在中文中，通常使用第一人称代词“我”指代自身。在计算机科学中，有著名的停机问题。计算机进程中的自指主要是为递归。

Self-reference occurs in natural or formal languages when a sentence, idea or formula refers to itself. The reference may be expressed either directly—through some intermediate sentence or formula—or by means of some encoding. In philosophy, it also refers to the ability of a subject to speak of or refer to itself: to have the kind of thought expressed by the first person nominative singular pronoun, the word "I" in English.