The term, Toy Dog, traditionally refers to a very small dog.  There are quite a few very small dog breeds that can include Spaniels, Pinchers and Terriers.  These dogs have been bred down in size.  The very smallest of them are called teacup dogs.  They are no more than 17 inches and weighs 4lbs or less.  Some can actually fit in a teacup.

Toy dog breeds include Terriers, Spaniels, Pomeranian, Chihuahua, Pug, Maltese, etc.  Some breeds come in different sizes, such as Poodles.  They come in standard, miniature and toy varieties.  Categories vary between countries and dog registries.  The Pug is probably the largest in the toy dog group and can weigh up to 18lbs.

It is wrongly assumed that toy dogs are only companion animals that are slow moving and do not need lots of exercise.  Although dainty and small they are quite capable of going on long walks with their owners and they enjoy their energetic dog agility.  These small dogs are examples of very robust daintiness.  Even though bred exclusively as pets, they can still hunt and play with pray.

Toy dogs may have their origins in the very ancient lapdog type, or they may be very small versions of working or hunting dogs.  These dogs are bred down for specific work or to create a convenient size pet.

In the past, very small dogs, not used for hunting, were used as watchdogs or kept as symbols of affluence.  Another function was to attract fleas from their owners.