Mystery novels are fictional books that are able to be classified in the "mystery" genre, typically revolving around a crime of some sort. Detective fiction is a well-known type of mystery novel, wherein the reader observes a detective attempting to solve a crime, such as a murder or kidnapping, throughout the course of the plot. The term "mystery novels" may be used as a description for most crime fiction, however. Edgar Allan Poe is one of the first and most well-known writers of mysteries, beginning in the mid-19th century.
In general, there are a few common types of mystery novels. The first, sometimes referred to as "whodunit," is a more classic type of mystery novel in which a person or group of people is attempting to solve a crime through figuring out a series of puzzling clues. These are also sometimes referred to as puzzle mysteries or cozy mysteries. The protagonist is typically an amateur detective without much experience solving crimes, and these books are typically fairly bloodless. They often take place in a small town or country home.
Another common type of mystery novel is a police procedural. In these types of mystery novels, the reader observes a police officer or police detective solving a crime by using common police methods. Police procedurals are often part of a series of mystery novels, where the same detectives will solve different crimes in each novel, but in a strikingly similar manner. Police procedural mysteries are somewhat grittier and more realistic than the "whodunits" above, and may contain more action and more detailed descriptions of crime scenes.
Finally, the third most common type of mystery novels is known as a hardboiled mystery. This type of novel generally features a detective working independently, usually slightly above the law. These are often the grittiest type of mystery novel, and feature a great deal of action, violence, and crime scene description that does not leave much to the imagination. Detectives in this group of mysteries often have somewhat shady pasts, though this is of course not always the case. Hardboiled mysteries are frequently serialized as well.
Mystery novels also frequently cross genres. For instance, a mystery novel may also include elements of romance. Supernatural mysteries are also quite popular, as are historical mysteries that are set sometime in the past. This genre of novel remains popular as ever, with many new mystery novels and short stories published every year.