High School DxD (Japanese: ハイスクールD×D, Hepburn: Haisukūru Dī Dī) is a Japanese light novel series written by Ichiei Ishibumi and illustrated by Miyama-Zero. The story centers on Issei Hyodo, a perverted high school student from Kuoh Academy who desires to be a harem king and is killed by his first date, revealed to be a fallen angel, but is later revived as a devil by the red-haired devil princess Rias Gremory to serve her and her devil family. Issei's deepening relationship with Rias proves dangerous to the angels, the fallen angels, and the devils. High School DxD began serialization in Fujimi Shobo's Dragon Magazine in its September 2008 issue. The first volume was released on September 20, 2008. A total of twenty five volumes is available in Japan as of March 2018 under their Fujimi Fantasia Bunko imprint. A manga adaptation by Hiroji Mishima began serialization in the July 2010 issue of Dragon Magazine and later in the March 2011 issue of Monthly Dragon Age with eleven volumes released.

Ishibumi has grouped the light novels into story arcs. The first arc, titled The Red Dragon Emperor's Awakening (赤龍帝覚醒, Sekiryūtei Kakusei), ran through the first two volumes. Birth of the Breast Dragon Emperor (乳龍帝誕生, Chichiryūtei Tanjō) is the second story arc and follows volumes three through six. The Heroic Oppai Dragon (英雄ヒーローおっぱいドラゴン, Hīrō Oppai Doragon) follows volumes seven through twelve.[LN 12 afterword] The fourth arc, The Legend of Oppai Dragon and his Lively Companions (おっぱいドラゴンと愉快な仲間たちの伝説, Oppai Doragon to Yukaina Nakamatachi no Densetsu), follows volumes fourteen through twenty-one.[LN 14 afterword] The fifth and final arc of the series, Red Dragon Emperor of the Blazing Truth × White Dragon Emperor of the Morning Star: The True Dragon(s) of the Kuoh Academy (燚誠の赤龍帝×明星の白龍皇 -駒王学園の真なる龍), starts at volume twenty-two and ends at volume twenty-five. The author has announced a sequel to the series, which began on July 20, 2018.

The light novels also feature a series of side stories set in between the main storyline and are often compiled into volumes. So far, three short story collections (Volume 8, Volume 13 and Volume 15) have been published.[LN 8][LN 13][LN 15]