Crime fiction is the literary genre that fictionalises crimes, their detection, criminals, and their motives. It is usually distinguished from mainstream fiction and other genres such as science fiction or historical fiction, but boundaries can be, and indeed are, blurred. It has several subgenres, including detective fiction (such as the whodunit), legal thriller, courtroom drama, and hard-boiled fiction. In Italy people commonly call a story about detectives or crimes “giallo”(en: yellow), because books of crime fiction have usually had a yellow cover since the thirties.