Mad, Bad and Dangerous to Know may refer to:
"Mad, bad, and dangerous to know", a phrase used by Lady Caroline Lamb (1785–1828) to describe her lover Lord Byron Mad, Bad and Dangerous to Know (Dead or Alive album), 1986 Mad, Bad and Dangerous to Know (EP by Joolz Denby with New Model Army), 1986 Mad, Bad, and Dangerous to Know (The Cross album), 1990 "Mad, Bad & Dangerous to Know", a 2005 song by Blue Tears from Mad, Bad and Dangerous Mad, Bad and Dangerous to Know, a 2008 book by Ranulph Fiennes Mad, Bad, Dangerous to Know: The Fathers of Wilde, Yeats and Joyce, a 2018 book by Colm Tóibín Mad, Bad & Dangerous to Know, a 2020 novel by Samira Ahmed
See also Mad, Bad and Dangerous?: The Scientist and the Cinema, a 2005 book by Christopher Frayling A Mad, Bad, and Dangerous People?: England 1783–1846, a 2006 book by Boyd Hilton