A toy dog is a very small dog kept as a pet, as compared to a very small working dog, although both pet and working dogs can be very small. Small dogs are wonderful and devoted companions as well as great family pets. You can find a small dog breed that is right for you no matter your lifestyle. They may be small in size but can be bold and make good watchdogs. You need to decide if you want a puppy who is adorable but will take a lot of time and attention or an older dog who is housebroken and obedience trained.
Toy dogs have become enormously popular over the years.  The Toy Group includes most of the very small and miniature lap dogs and apartment-sized companion dog breeds. There are many small and toy breeds that make excellent pets for small homes. Toys are popular companion dogs for people living in cities and adapt well to apartment life.

These toy dogs boast unique character and charm, and make ideal pets and companions for many people and households. Another area of contention is the idea that toy dogs are only companion animals, slow moving, with little need for exercise and with low endurance.
The use of the word "toy" to describe small dogs that belong to a toy breed is redundant and also incorrect, suggesting that the breed comes in different sizes - there is no such thing, for example, as a "toy Chihuahua"; all Chihuahuas are toy dogs. (However, some breeds do come in different sizes, such as Poodles, which come in standard, miniature, and toy varieties).

Ten Most Popular Toy Dog Breeds :

The most popular small dog breeds are : Chihuahuas, Pugs, Maltese, Yorkies and Toy Poodles. 

Based upon statistics from the American Kennel Club, the top ten toy dog breeds include :

Chihuahuas : The Chihuahua is a good apartment dog but enjoys exercising and playing outdoors on warm day. They should be protected when outdoors in cool or cold weather with a sweater. The tiny and very pretty Chihuahua is a dog that has plenty of character, and is a devoted and charming dog that offers love, entertainment, loyalty, and excellent companionship. This is a very confident breed that knows how to stand up for itself yet enjoys plenty of fuss and attention from its owners.  These dogs are perfect for the elderly or an individual because they make wonderful companions. They are loyal and have an affinity for being close to their master. You need to watch their diet because they tend to gain weight easily.
They only weigh between 2-6 pounds.

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Cavalier King Charles Spaniel : A regal and graceful looking animal, the Cavalier King Charles Spaniel is a dog with a gentle and agreeable and even temperament, and is a loving, loyal, and loveable companion. They are an extremely patient dog and so eager to please you. Energetic and playful, this devoted breed loves to be in the thick of the action and enjoys plenty of fuss and attention from humans. They are outgoing, playful and want to be loved. 
Weight: 10-18pounds

Yorkshire Terriers : A Yorkie is a lively and lovable companion. They are affectionate, highly energetic, clever and make a good watchdog. This alert and intelligent looking breed is strong, energetic, and loyal, and is like a big dog in a small package. Although they can be stubborn and are more suited to families with older children rather than boisterous youngster, this is a small dog that can bring real pleasure and entertainment as well as providing excellent companionship. They do need daily brushing. He only weighs between 5-7 pounds but he is fearless.
Yorkshire Terrier Breed, click here

Shih Tzu : The Shih Tzu is a sturdy and robust toy dog, with bags of character and a playful, confident, and bubby personality. One of the oldest breeds, they are a graceful toy dog. They are very engaging, sweet and spunky dog. They have a strong sense of self so would be a poor choice for a family with babies or small children since he tends to be jealous of them.He's a fine companion for older children. The Shih Tzu is a very elegant and pretty dog. He is a very loyal and friendly dog. They only weigh between 9-16 pounds.

Pugs : He is a favorite with children and is just a great dog to have live with you. Pugs have a very distinctive and unique look and appearance, and are robust and sturdy little toy dogs with plenty to offer. The pug makes a great companion, and is playful, energetic, and full of character. He loves to please you, is fun loving, even-tempered, outgoing and playful.
Weight: 14-18 pounds

Maltese : The Maltese is a beautiful looking dog, and is also great for those with pet related allergies because of reduced hair shedding and dander. The Maltese needs daily combing and brushing, bathed regularly and clean eyes daily.  This breed is great for apartment living.  They were bred for companionship so they don't like to be left alone for long hours. This breed is loyal, loving, and dedicated, as well as making wonderful companions. They also do well with other animals. Basic obedience training is sufficient because they are naturally obedient.
Weight: 4-6 pounds

Papillon : These dogs are eager to please and rank #1 toy dog in obedience.  Lively, affectionate, intelligent, and charming, the Papillon is a breed that offers excellent companionship and boasts plenty of character and charm. Papillons are hearty, spirited and make good watchdogs.  This is a robust and attractive breed that will lavish its owners with love and attention, as well as providing plenty of entertainment. If socializated early with cats they are okay and get along with smaller dogs but may challenge bigger ones. Although not yappy but will bark at sights and sounds to alert their family to danger and visitors. They have an alert and intelligent expression.
Weight: 3-9 pounds 

Miniature Pinschers : The Miniature Pinscher is a spirited and lively toy dog that boasts bags of courage and character. These fun-loving extroverts make good family pets and excellent companions. The Miniature Pinscher needs to be near people not left alone for long periods of time. They learn easily and well learn fast to obey you because they want to please you. They have high energy and like to bark. Although this breed can be stubborn and won't always get along with other dogs, the Miniature Pinscher does offer excellent companionship and is ideal for those looking for an entertaining, loving, and loyal pet.  They are so curious and love to investigate everything and will go to great lengths to do it. They will escape whenever possible. Weight: 8-10 pounds

Pomeranians : One of the smallest of the toy dog breeds, the cute and lively. Poms do well in apartment living or small house. Pom is a wonderful pet for those looking for companionship and the affections of a loyal and loving dog.  Intelligent, eager, and entertaining, this breed makes a great addition to the household. They are loyal to their owner and eager to learn. They are an excellent indoor dog that only require light activity like a short walk.
Weight: 3-7 pounds

Toy Poodles : The miniature and toy are the most popular. They are a highly intelligent, good-tempered, extremely people-oriented and happy dogs. These dogs make excellent companions, and are always ready to shower their owners with love, attention, and devotion.
Weight: 4-9 pounds