Baccano is a light novel written by Ryogo Narita with illustrations by Katsumi Enami. "Baccano", which author Narita translates as "stupid commotion", is Italian for "ruckus". Each of the stories in the series involves several unrelated plots intersecting and crossing each other as events spiral farther and farther out of control - Immortal alchemists, mafia operated speakeasies, and many other elements of pulp fiction mashed together, creating a world straight out of the movies.
Source: http://www.baka-tsuki.org/project/index.php?title=Baccano