Monthly Afternoon is a Japanese monthly seinen manga anthology published by Kodansha under the Afternoon line of magazines. The first issue was released with a cover date of January 25, 1986. Afternoon has spawned many successful manga series such as Oh My Goddess!, Genshiken, Blade of the Immortal and Big Windup!. It is part of Kodansha's "1day" series, which also includes the magazines Morning and Evening. A spin-off magazine, named good! Afternoon, started publishing on November 7, 2008.

Kodansha Ltd. is a Japanese privately held publishing company headquartered in Bunkyō, Tokyo. Kodansha publishes the manga magazines Nakayoshi, Afternoon, Evening, Weekly Shōnen Magazine, and Bessatsu Shōnen Magazine, as well as the more literary magazines Gunzō, Shūkan Gendai, and the Japanese dictionary Nihongo Daijiten. Kodansha was founded by Seiji Noma in 1910, and members of his family continue as its owners either directly or through the Noma Cultural Foundation.