A Cruel Angel's Thesis

"A Cruel Angel's Thesis" (残酷な天使のテーゼ, Zankoku na Tenshi no Tēze) is a J-pop song performed by Japanese singer Yoko Takahashi and the opening theme of the anime television series Neon Genesis Evangelion. The song was composed by Toshiyuki Ōmori and Hidetoshi Satō, with its lyrics written by Neko Oikawa. It was released as a double-A-side single with "Fly Me to the Moon", the show's closing theme, on October 25, 1995. "The Cruel Angel's Thesis" was also included in the series' soundtrack releases and Takahashi's albums.

The song received acclaim from music critics and audiences alike; it later became one of the most famous Japanese anisongs, songs specially created for anime series. Years after the show's first airing, "The Cruel Angel's Thesis" has remained a popular Japanese karaoke song, winning popularity polls and awards. On the Internet, along with its official video, the song gained further fame through covers and parodies, becoming one of the most famous theme songs in the history of anime.