Nostalgia: Op.3 (Op.3 meaning the third opus) is a piano based rhythm game in Konami's BEMANI franchise. It is the third game in the Nostalgia series and a spiritual successor to Konami's Keyboardmania series.

The game consists of falling bars corresponding to certain areas of the keyboard. When the bars cross the judgement line it is time to play that key. There are three type of notes - Normal note which you play as normal, slide note where you slide your hand across the keyboard and trill note where you rapidly and alternately press two neighbouring keys.

Op.3 adds more sorting functionality to the song selection screens, which is needed as the song list has grown in size. It also allows you to filter on your scores and grades, making it easier to improve your overall skill level in the game. Recital mode is now a toggle on the standard mode instead of another mode.

This is the first time in the series where some songs are not carried over from previous version, due to licenses not being renewed. 75 songs were brought forward from Nostalgia, 97 from Nostalgia: Forte and 126 from Nostalgia: Op.2. Along with the 49 new songs in Op.3, that brings the total song list up to 347 songs (as of 27th June 2020). Since this is an currently active game, the song list will likely expand up until the release of the next game in the series.