The World's Greatest First Love: The Case of Ritsu Onodera (世界一初恋 〜小野寺律の場合〜, Sekai-Ichi Hatsukoi: Onodera Ritsu no Baai, also alternatively known as Sekai Ichi Hatsukoi: The World's Greatest First Love in the English anime) is a Japanese BL manga series written and illustrated by Shungiku Nakamura. In 2011, the manga was adapted into an anime television series. Produced by Studio Deen under the direction of Chiaki Kon, the anime series began its broadcast run on April 9, 2011. An original animation DVD was bundled with the fifth and sixth volumes of the manga series, released in March and September 2011. A film adaptation was released on March 15, 2014.

On December 13, 2016, Funimation announced they had licensed the series, including the OVA. It was released on home-video on March 7, 2017.

In January 2018, the manga has launched the game app version, which was released for the Smartphone/iOS.

A new anime adaptation focused on the Proposal Arc has been announced to celebrate the fifth anniversary of the new Emerald magazine. It premiered on February 21, 2020. In June 2021, the anime was revisited by Funimation's Aedan Juvet where it was praised for its expansion of LGBTQ+ representation in anime.

Sekai-ichi Hatsukoi is a spin-off of Junjo Romantica, another series by the same author.