Toby is a dog used by Sherlock Holmes on occasion to follow scent trails. He is described by John Watson as a "ugly long haired, lop-eared creature, half spaniel and half lurcher, brown and white in colour, with a very clumsy waddling gait."
- Toby appears in the 1978 non-Canon novel Sherlock Holmes vs. Dracula; or, The Adventures of the Sanguinary Count, by Loren D. Estleman.
- Toby appeared in the 1960s BBC series' 1968 adaptation The Sign of Four, the penultimate episode of the entire series. He was played by a dog called Toddy.
- In the Granada Television series' 1987 feature-length special The Sign of Four, Toby plays a major role in the storyline, similarly to the novel. He's acquired from Mr Sherman and aids Holmes and Watson in their investigation. Toby's animal actor is a slightly different cross-breed than in the novel, apparently a cross between a spaniel and a border collie (rather than a lurcher). A reference to Toby also appears on the series' sole official soundtrack release from 1987, in the form of the track Old Sherman's Dog Toby.  
- In Sherlock, there are two different animal characters named Toby. One is a tomcat named Toby, owned by Molly Hooper, who only appears off-screen on Molly's fictional blog. The other is a bloodhound named Toby, borrowed from a hacker named Craig and briefly used by Sherlock, John and Mary during an investigation. However, unlike the original version of the character, Sherlock's Toby the dog appeared in The Six Thatchers, a loose adaptation of The Adventure of the Six Napoleons (albeit with elements from The Sign of the Four, previously adapted by the series as The Sign of Three).
- Toby appears in both the novel and film The Seven-Per-Cent Solution, where Sherlock Holmes makes use of the dog and a bottle of vanilla extract to track Professor Moriarty to Austria.
- Toby appears as a playable character in the video game Sherlock Holmes: Crimes & Punishments and its sequel Sherlock Holmes: The Devil's Daughter.