The Yorkshire Terrier breed standard specifies that the dog should have a compact, athletic build suitable for an active lifestyle; and hold itself in an upright, confident manner. The Yorkie has a free, jaunty gait, with both head

and tail held high.  For Yorkies, toy stature does not necessarily mean frail or fragile.

Appearance: Yorkshire Terriers are a long-haired breed with no undercoat, which means that they do not shed as much as their short haired friends. Rather, their hair is like human hair in that it grows continuously and falls out rarely (only when brushed or broken). Additionally, since Yorkies carry less dander on their coat, they generally do not have the unpleasant "wet dog" odor when wet, and they may not affect as many people who suffer from dog-related allergies.

Yorkie puppies are born with a black and tan coat, and normally have black hairs mixed in with the tan until they are matured. The breed standard for adult Yorkies places prime importance on coat color, quality and texture. The hair must be glossy, fine and silky. However, some have very fine hair, making it feel a bit different and are harder to care for. From the back of the neck to the base of the tail, the coat should be a dark steel-blue (not silver-blue)- never mingled with fawn, bronze or black hairs. Hair on the tail should be a darker blue.On the head, chest and legs, hair should be a bright, rich tan, and darker at the roots than in the middle, shading to still lighter tan at the tips. Some Yorkies never turn the usual blond and continue to be gray. There should be no dark hairs intermingled with any of the tan in adult dogs.Many Yorkies do not conform to the standard for coat color; the tan may range from a very light blonde to a darker brown, while the body may be black or silvery gray. Many pet-quality Yorkies have "wooley" coats which are completely black across the back. The hair never "breaks" into the dark steel blue that is preferred in the breed because the coat texture is not a pure silk - the favorable coat texture. The Yorkie’s nose, lips, eye-rims, paw-pads and nails should be darkly pigmented.

The breed standard requires that the Yorkshire Terrier's hair be perfectly straight (not wavy). For show purposes, the coat is grown-out long and parted down the middle of the back, but may be trimmed to floor length to give ease of movement and a neater appearance. Hair on the feet and the tips of ears are also be trimmed. The traditional long coat is extremely high maintenance, requiring hours of daily brushing. To maintain the long coats of show dogs (between exhibitions), the hair may be wrapped in rice paper, tissue paper or plastic, after a light oiling with a coat oil made for show coats, which prevents the hairs from being broken easily and keeps the coat in condition. The oil has to be washed out once a week and the wraps must be fixed periodically during the week to prevent them from sliding down and breaking the hair. As a more practical alternative, many Yorkie-owners opt to keep the dog's coat trimmed to a shorter all-over length.

Modifications: Often, a Yorkie’s dewclaws, if any, are removed.Traditionally, the Yorkie’s tail is docked to a medium length. In America, almost all breeders dock the tails of puppies. However, since the 1990s there has been a growing movement to ban the practice of cosmetic docking. The World Small Animal Veterinary Association and the European Convention for the Protection of Pet Animals oppose tail docking. As of 2007, several nations have enacted prohibitions on docking, including Australia, Belgium, Cyprus, Finland, Germany, Greece, Luxembourg, Norway, South Africa, Sweden and Switzerland.

Temperment: Though a toy breed, the Yorkie still retains much of its terrier ancestry in terms of personality. Individual dogs will differ, but they are generally intelligent, independent and courageous. Yorkshire Terriers are quick to determine where they fit in a household's "pack. Their behavior towards outsiders will vary - they often will be inclined to bark at strangers, but some Yorkies are outgoing and friendly towards new people while others are withdrawn and aloof. The differences in behavior in this regard are largely based on how the owner trains or conditions (and socializes) the Yorkie. A few individual Yorkshire Terriers may be timid or nervous, rather than bold, but the vast majority do seem to meet the breed standard for a confident, vigorous and self-important personality.

Boldness: In a multi-breed home, many Yorkies will assert themselves as the "alpha" dog. Yorkies typically get along well with other dogs and love to play together with them. Rather, bold character comes from the Yorkie's mix of great inquisitiveness, or an instinct to protect, and self-confidence. Some Yorkies are unaware of their small size and may even challenge larger, tougher dogs. In one case a 12-pound Yorkie pushed open a screen door (to investigate a commotion outside) and rushed to the aid of an elderly woman who was being attacked by an 80-pound Akita. When the Yorkie snapped and growled, the Akita turned his attention on the small dog long enough for the woman to escape. Unfortunately, this boldness can get Yorkies into trouble, as small dogs can be seriously injured. For similar reasons, Yorkies do not make suitable pets for very young children.

Yorkshire Terriers as a breed are intelligent dogs. According to Dr. Stanley Coren, an expert on animal intelligence, the Yorkshire Terrier is an above average working dog, ranking 27th (32nd including ties) out of the 132 breeds tested. His research found that an average Yorkshire Terrier could understand a new command after approximately 15 repetitions and would obey a command the first time it was given 70% of the time or better. This capacity as working dogs enables Yorkies to excel in sports like obedience and agility, which require the dog to understand communication from the handler and carry out a complex series of commands. Additionally, Yorkies learn to recognize numerous words and can be taught to distinguish and fetch separate toys in a box by their names.

The well bred and well handled Yorkshire Terrier is content to be near its owner without being on a lap or underfoot. Yorkies are energetic, but also need much rest and will often prefer to spend downtime in privacy, such as in a kennel or out-of-the-way corner. Early terriers were expected to hunt in the company of handlers and other dogs, but also to have the self-confidence to go out on their own after prey. Very pampered and indulged Yorkies are more likely to be clingy and demanding, and lack the true terrier self-confidence. Yorkshire Terriers tend to be more difficult to train than some breeds, due to their characteristic independent nature. The independent mindedness of Yorkies leads some trainers to consider them to be among the hardest to house-break

Health: Health issues often seen in the Yorkshire Terrier include bronchitis, lymphangiectasia, hepatic lipidosis, cataracts and keratitis sicca. Additionally, injection reactions (inflammation or hair loss at the site of an injection) are common. Yorkies often have a delicate digestive system, with vomiting or diarrhea resulting from consumption of foods outside of a regular diet. They are usually picky with which foods they eat. They usually will not eat what they don't like, it will be left aside. Trying to mix foods is not a good idea because they tend not to enjoy it.The relatively small size of the Yorkshire Terrier means that it usually has a poor tolerance for anesthesia. Additionally, a toy dog such as the Yorkie is more likely to be injured by falls, other dogs and owner clumsiness. Due to their small size, Yorkies may be endangered if kept in the house with an undiscerning or abusive person, especially a child. Many breeders and rescue organizations will not allow their Yorkies to go to families with young children, because of the risk it poses to the dog.

The life span of a healthy Yorkie is 12-15 years. Under-sized Yorkies (3 pounds or less) generally have a shorter life span, as they are especially prone to health problems such as chronic diarrhea and vomiting; are even more sensitive to anesthesia; and are more easily injured.

Hypoglycemia: Low blood sugar in puppies, or transient juvenile hypoglycemia, is caused by fasting (too much time between meals). In rare cases hypoglycemia may continue to be a problem in mature, usually very small, Yorkies. It is often seen in Yorkie puppies at 5 to 16 weeks of age. Very tiny Yorkie puppies are especially predisposed to hypoglycemia because a lack of muscle mass makes it difficult to store glucose and regulate blood sugar. Factors such as stress, fatigue, a cold environment, poor nutrition, and a change in diet or feeding schedule may bring on hypoglycemia. Low blood sugar can also be the result of a bacterial infection, parasite, or portosystemic liver shunt. Hypoglycemia causes the puppy to become drowsy, listless (glassy-eyed), shaky and uncoordinated, since the brain relies on sugar to function. Additionally, a hypoglycemic Yorkie may have a lower than normal body temperature and, in extreme cases, may have a seizure or go into a coma. A dog showing symptoms should be treated by a veterinarian immediately, as prolonged or recurring attacks of hypoglycemia can permanently damage the dog’s brain. In severe cases it can be fatal.

Genetic defects: As with many purebred dogs, the Yorkshire Terrier is prone to certain genetic disorders, including distichiasis, hydrocephalus, hypoplasia of dens, Legg-Perthes disease, patellar luxation, portosystemic shunt, retinal dysplasia, tracheal collapse and bladder stones.The following are among the most common congenital defects that affect Yorkies.

• Distichiae, eyelashes arising from an abnormal spot (usually the duct of the meibomian gland at the edge of the eyelid), are often found in Yorkies.Distichiae can irritate the eye and cause tearing, squinting, inflammation, and corneal abrasions or corneal ulcers and scarring. Treatment options may include manual removal, electrolysis or surgery.

• Hypoplasia of dens is a non-formation of the pivot point of the second cervical vertebra, which leads to spinal cord damage.Onset of the condition may occur at any age, producing signs ranging from neck pain to quadriplegia.

• Legg-Perthes disease, which causes the top of the femur (thigh bone) to degenerate, occurs in Yorkies more than in any other breed. The condition appears to result from insufficient circulation to the area around the hip joint.As the blood supply is reduced, the bone in the head of the femur collapses and dies and the cartilage coating around it becomes cracked and deformed. Usually the disease appears when the Yorkie is young (between five and eight months of age); signs are pain, limping or lameness. The standard treatment is surgery to remove the affected part of the bone. Following surgery, muscles hold the femur in place and fibrous tissue forms in the area of removal to prevent bone rubbing on bone. Although the affected leg will be slightly shorter than prior to surgery, the Yorkie may regain almost normal use.

• Luxating patellas (slipping kneecaps) are another common genetic defect in Yorkies. Weak ligaments and tendons in the knee or malformed (too shallow) patellar grooves, allow the patella to slip out of its groove sideways. This causes the leg to 'lock up' with the foot held off the ground.A dog with this problem may experience frequent pain and lameness or may be bothered by it only on occasion. Over time, the patellar ridges can become worn down, making the groove even more shallow and causing the dog to become increasingly lame. Surgery is the main treatment option available for luxating patellas, although it is not necessary for every dog with the condition.

• Portosystemic shunt, a congenital malformation of the portal vein (which brings blood to the liver for cleansing), is also common in Yorkies. In this condition some of the dog's blood bypasses the liver and the “dirty” blood goes on to poison the heart, brain, lungs and other organs with toxins. A Yorkie with this condition might exhibit a wide variety of symptoms, such as small stature, poor appetite, weak muscle development, decreased ability to learn, inferior coordination, occasional vomiting and diarrhea, behavioral abnormalities, seizures (especially after a meal), blindness, coma and death. Often the shunt can be treated with surgery.

• Tracheal collapse, caused by a progressive weakening of the walls of the trachea, occurs in many toy breeds, especially very tiny Yorkies. As a result of genetics, the walls of the trachea can be flaccid, a condition that becomes more severe with age. Cushing's disease, a disorder that causes production of excess steroid hormone by the adrenal glands, can also weaken cartilage and lead to tracheal collapse. There is a possibility that physical strain on the neck might cause or contribute to trachea collapse. Since this is usually caused by an energetic Yorkie pulling against his collar, many veterinarians recommend use of a harness for leashed walks. An occasional “goose honking” cough, especially on exertion or excitement, is usually the first sign of this condition. Over time, the cough may become almost constant in the Yorkie’s later life.Breathing through the obstruction of a collapsed (or partially collapsed) trachea for many years can result in complications, including chronic lung disease. The coughing can be countered with cough suppressants and bronchodilators. If the collapse is advanced and unresponsive to medication, sometimes surgery can repair the trachea.