- O cachorro que sabia miar
- O' Artful Death
- Oak
- Oberwasser
- Objets d'Artifice
- Occult and Battery
- Oceans & Potions
- Och aldrig jag lämnar dig åter
- Octopus
- Octubre
- Odds on Miss Seeton
- Odjur
- Of Birds and Beagles
- Of Books and Bagpipes
- Of Murder and Men
- Of Potions and Portents
- Of Spice and Men
- Of Stars and Spells
- Off Kilter
- Off the Books
- Off With His Head
- Offed in the Orchids
- Oggetti Smarriti
- Oh Danny Boy
- Oh Holy Fright
- Oh Say Can You Fudge
- Oh, Fudge!
- Oh, No, Octavius!
- Oh, Shoot!
- Oktoberfest
- Old Age Private Oh My!
- Old Bones Can Be Murder: Charlie Parker Mysteries: A Between-the-Numbers Novella
- Old Dog New Tricks
- Old Fashioned Crooks
- Old Haunts
- Old Jewels
- Olivia Faulkner Mysteries Box Set Vol 1: Books 0.5-3
- Olivia Thompson Mysteries Box Set One
- Oltrepassare la Linea
- Omicidio in alto mare
- Omit Flowers
- On Borrowed Crime
- On Borrowed Time
- On Deadly Tides
- On Mother Brown's Doorstep
- On Pins and Needles
- On Skein of Death
- On St. Nick's Trail
- On The Bayou
- On the Buckle, Dream Horse Mystery #1
- On the Hook
- On the Hunt
- On the Lamb
- On The Mountain Of Hope
- On the Road to Ordinary
- On the Rocks (A Ruby Steele Mystery—Book 1)
- On the Rocks (Ein Cozy-Krimi mit Ruby Steele – Buch 1)
- On the Scent
- On the Slam
- On the Street Where Death Lives
- On the Street Where You Live
- On The Wagon
- On Thin Icing
- Once and Always Murder
- Once Cursed, Twice Shy: A Cozy Magical Fantasy Adventure
- Once Ghosted, Twice Shy
- Once Upon A Coven
- Once Upon a Murder
- Once Upon a Murderous Retreat
- Once Upon a Seaside Murder
- Once upon a Spine
- Once Upon a Trailer Park
- Once You Go Black
- One Bad Apple
- One Book in the Grave
- One Corpse Open Slay:A Witchy Christmas Cozy Mystery
- One Cup Of Flour Two Cups Of Murder
- One Dead Cookie
- One Dead Vampire
- One Deadly Date
- One Fete in the Grave
- One Flew Over the Chow-Chow's Nest
- One Foot in the Grove
- One for the Books
- One for the Hooks
- One Good Eclair (A Nutrition Mafia Mystery)
- One Good Turn
- One Hot Murder
- One Minute to Midnight: Magic and Mayhem Universe
- One Night In Sedona
- One Night in the Bayou
- One of My Sons
- One Perfect Line
- One Poison Pie
- One Potato, Two Potato, Dead
- One Potion in the Grave
- One Woman's Junk
- Only By Moonlight
- Only Skein Deep
- Only the Cat Knows
- Oolong, Farewell
- Oopsy Daisy
- Op Zoek Naar Ariadne
- Open for Murder
- Opening Night
- Opera Cake Murder
- Operation Washtub
- Or Was He Pushed?
- Orange sanguine
- Oreo Girls
- Organize Your Corpses
- Organized for Christmas Wishes
- Organized for Homicide
- Organized for Masked Motives
- Organized for Murder
- Organized for Picnic Panic
- Organized Murder
- Organized Mysteries Collection Vol. 1: 3 Book Box Set
- Original Sin
- Orion's Foot: Myth, Mystery, and Romance in the Amazon
- Ornaments of Death
- Orphaned in Cherry Hills
- Os Deseguamos unas Mortales Navidades
- Osterwasser
- Ostfriesenmelodie
- Ostfriesisch kriminelle Weihnacht: 25 Krimis und 25 Rezepte
- Ostsee Krimi Sammelband: Rügener Abgründe und Rügener Haie
- Our Second Civil War
- Ouragan sur la mémoire
- Out at Second Base
- Out Like a Goddess
- Out of Circulation
- Out of Control
- Out of Hounds
- Out Of The Blue
- Out of the Darkness
- Out of the Dying Pan
- Out of the Rain
- Out Of The Shadows
- Out of the Storm
- Out on a Limb
- Out With The Old and Death
- Outfoxed
- Over My Dead Body
- Over the Edge: Murder Returns to the Caribbean
- Overboard on the Ocean
- Overdosed in Cherry Hills
- Overdue
- Overdue for Murder
- Overkill (The Belinda & Bennett Mysteries, Book Four)
- Overture to Death
- Owl Be Home for Christmas
- Owls Well That Ends Well
- Oxford Blue
- Oy Vey, Maria! A Mrs. Kaplan Mystery
- Oyster Spat, a Sylvia Avery Mystery, Book 5