Amateur Sleuth
An Amateur Sleuth mystery features a main investigative character who does not do professional sleuthing for a living (not a Detective or Police Officer, for example). The Amateur Sleuth can be a person of any age, gender, or profession who usually stumbles upon a mysterious situation, investigates the evidence, and ultimately solves a mystery through various (and often creative and unconventional) techniques, with or without the help of law enforcement.

Chick Lit
Chick Lit initially was defined as a literary term for a work of fiction that appeals to a target audience of young women, specifically single, working women in their twenties. However, in recent years, Chick Lit novels have found an increased audience of women (and even some men) of all ages and lifestyles, though the stories usually feature one strong female lead character, and the style of the genre remains centered around (though not limited to) common urban themes such as dating, shopping, sex, fashion and the workplace.

Cozy
Traditionally, a cozy was not just a lighter mystery without blood, gore, or sex with an amateur sleuth. In traditional cozies the rules of fair play are observed. That is, the reader is given all the clues needed to solve a mystery before the end of the book. Readers today are more likely looking for a nice, entertaining, clean story rather than an intellectual exercise, so the rules of "fair play" are considerably relaxed. Agatha Christie's Miss Marple and Jesica Fletcher from Murder She Wrote are examples are cozy sleuths.

Cuisine
A book in this genre features a mystery in which food is well-integrated into the storyline, either peripherally or directly into the plot. The book might take place in a restaurant, feature recipes, or just discuss food in a consistent manner that is vital to the story.

Hard-Boiled
A hard-boiled story is tougher and grittier than soft- or medium-boiled stories. They often incorporate violence, no-holds-barred descriptions of crime scenes, and sexual encounters. They usually feature a lone-wolf private detective who is cynical yet quixotic. Think Sara Paretsky, Ian Rankin, Raymond Chandler, Michael Connelly, James Elroy, Clyde Ford (The Long Mile).

Historical
Historical mysteries are set in some time other than the present. Beyond that, they can be cozy or soft-boiled. It's rare to see medium- or hard-boiled historical. Think Ann Perry, Elizabeth Peters, Deborah Woodworth, M. J. Zellnik (Murder at the Portland Variety).

Medium-Boiled
Packs more punch than a cozy or soft-boiled but is not too tough or graphic in tone and description. Think Nevada Barr, Dana Stabenow. Usually, but not always, amateur sleuth.

Pets & Animal Friends
As you may have guessed, mysteries in this genre specifically feature one or more furry (or feathered, or scaled, or whatever!) friends who contribute directly to the plot of the story. In many cases, especially clever animals and pets assist the main characters in solving mysteries in unique, fun ways!

Regional
Some say that any story not set in LA or NY is a regional. Typically, stories that take the reader some place, stories where the location becomes a sort of character, stories where the location is a large part of the hook are called regionals. William Kent Krueger is good example of a regional.

Suspense
A Suspense mystery (often called a "Thriller") is a mystery that creates a feeling of tension and uncertainty. When you're reading a book with this kind of tension, it's tough not to feel intensely interested in the outcome, and feel a kinship with the main characters. These are "page-turner" books that keep you up all night in a constant state breathtaking entertainment, furiously reading to find out what happens next.