The Griffon Bruxellois, or Brussels terrier, is one of the quaintest and most attractive toy dogs found in this country. "Griffon", which many people think means terrier, merely means rough-haired; for instance, the Griffon Nivernais is very similar in size and shape to the old Welsh otter hound, and in fact a pack of these hounds came to England in the Franco-German War of 1870 and became absorbed in our Welsh packs. Griffons, or rough-looking terriers and spaniels, are much used for shooting in France.
The Griffon Bruxellois is a toy dog which has a great vogue in Belgium. The peasants there use any bitch, whether of 4 lbs. Or 10 lbs., but only use the very smallest dogs, for, as in the case of the most toy dogs, whether Pekingese, Pug or other variety, the big bitches mated to small dogs may produce three or four small puppies, but a miniature bitch will often produce one puppy, and that a large one.
£30 to £40 is a common price for a really small dog in Belgium, whereas a useful brood bitch can be bought for £2 to £3.
Though pets, they have terrier character and are often very sporting. The colour is usually red, sometimes black, and there are two varieties, rough and smooth. The smooth are known in Belgium as Brabançons. They are hardly a pure breed. The famous French sportman, Count Couteulx de Canteleu says that no really pure breed produce puppies with dewclaws, and quotes the Griffon as an impure breed of dog. As, however, he applies this description to the British Foxhound for the same cause I am inclined to doubt his reasoning.
Griffon breed true in character if not in size, and, as in all toys, it is very difficult to get them all level, as apart from other considerations, food and exercise all play their part far more in a breed like the Fox terrier.
Though not comparable to the Pekingese in popularity, yet they are one a ready market at remunerative prices for well-bred stock.

General Appearance: Sprightly, robust, reminding one of a cob.
Head: Large and rounded with rather coarse hair.
Nose: Always black, short as possible, wide in nostril, muzzle in no way pinched.
Eyes: Very large, black or nearly black; eyelids edge with black.
Chin: Prominent without showing the teeth, and furnished with a bear if rough; jaw well undershot.
Texture of Coat: Harsh and wiry, free from curl or wave.
Colour: Red, black and tan, or black.
Chest: Rather wide and deep; back short.
Ears: Semi-erect, the smaller the better.
Tail: Docked, set on high.
Weight: Most desirable weight 6 to 9 lbs.
Faults: Pale eyes, silky tuft on head, showing teeth.
Disqualifications: Brown nose, white marks, tongue protruding.

At present bitches fetch higher prices than moderate quality dogs, unless too small to breed from.

Taken from: "Pedigree Dog Breeding for pleasure or profit and where to buy a dog"
Captain Jocelyn Lucas, M.C. UK, 1925