Cozy mysteries began in the late 20th century as a reinvention of the Golden Age whodunnit; these novels generally shy away from violence and suspense and frequently feature female amateur detectives. Modern cozy mysteries are frequently, though not necessarily in either case, humorous and thematic (culinary mystery, animal mystery, quilting mystery, etc.)
Detective fiction is a branch of crime fiction that centers upon the investigation of a crime, usually murder, by a detective, either professional or amateur. Detective fiction is the most popular form of both mystery fiction and hardboiled crime fiction.
Hardboiled crime fiction refers to a literary style pioneered by Carroll John Daly in the mid-1920s, popularized by Dashiell Hammett over the course of the decade, and refined by Raymond Chandler beginning in the late 1930s. Hardboiled fiction, most commonly associated with detective stories, is distinguished by an unsentimental portrayal of crime, violence, and sex.
The police procedural is a sub-genre of the mystery story which attempts to convincingly depict the activities of a police force as they investigate crimes. Unlike typical detective novels, which concentrate on one crime, police procedurals frequently show how police officers work to solve multiple crimes simultaneously.
