Floor Jansen (Dutch pronunciation: [ˈfloːr ˈjɑnsə(n)]; born 21 February 1981) is a Dutch singer and songwriter. She is the third and current lead vocalist of Finnish symphonic metal band Nightwish.

Jansen first became known as the lead vocalist of symphonic metal band After Forever from 1997, when she joined at age 16, to their disbanding in 2009. When After Forever disbanded, she formed ReVamp and has released two albums with them. In 2012 following the departure of their lead vocalist Anette Olzon, Nightwish brought in Jansen as a touring member until the end of their Imaginaerum World Tour. In 2013, they announced Jansen was now their full-time lead vocalist; she subsequently disbanded ReVamp to focus on Nightwish. In 2018, she and Pagan's Mind guitarist Jørn Viggo Lofstad premiered their hard rock duo Northward.

A frequent collaborator of Arjen Anthony Lucassen, Jansen is a member of his progressive metal supergroup Star One, and sang in the Ayreon albums Universal Migrator Part 1: The Dream Sequencer, 01011001, and The Source, as well as the live album Ayreon Universe – The Best of Ayreon Live. She also sang lead vocals in several songs of the MaYan album Quarterpast and in Avalon's Angels of the Apocalypse. She is the older sister of fellow singer Irene Jansen, who also worked with Ayreon.