Giallo

A cycle of stylish, psychosexually loaded Italian crime films which peaked sometime in the late '70s. The name means "yellow," and refers to the yellow covers of the pulp detective novels which were adapted into the first of the films. Gialli are generally plotted as "puzzle" mysteries (with either police or amateurs investigating), but with a heavy admixture of horror and thriller elements.

Major directors of gialli include Dario Argento, Mario Bava, and Lucio Fulci.

Many American movies have been influenced by gialli. These include Basic Instinct, Kill Bill, Vol. 2 (when it isn't being a Spaghetti Western), the Hostel movies, and pretty much anything by Brian De Palma. Slasher Movies have their roots in the giallo sensibility, as well. All quite appropriate, considering the considerable stylistic influence the genre draws from Alfred Hitchcock—to the point that many have deemed Hitch the unofficial "father" of Giallo cinema.

And now you too can create your own, with the Do-It-Yourself Giallo Kit.

A related genre is the German "krimis".

Common tropes include:

Acquitted Too Late
Animal Motifs
Conspicuous Trenchcoat: the default outfit for Giallo killers is a black leather coat with matching fedora and gloves, and sometimes a mask
Death by Sex
Drop Dead Gorgeous
Everyone Is a Suspect
Film Noir: Somewhat comparable to this genre, but much more colorful, surreal, and gory.
Freudian Excuse
Going by the Matchbook
Hand of Death: Almost always the black-gloved version.
Kensington Gore
Mood Lighting
Motive Rant
Never One Murder
Overly Long Title: Sometimes, titles are whole sentences. Example - Your Vice Is a Locked Room and Only I Have the Key
Peek-a-Boo Corpse
Police are Useless: if the main character is a civilian trying to solve the murders on their own, the cops will never figure it out first
Red Herring: Often an incredibly cheap variety in which one character is clearly extremely suspicious, creepy and weird and end up dead like any other victim without so much as a Hand Wave as to their odd behavior.