It has a white double coat of fur which fills out the dog's face, giving it a rounded appearance.

It is an energetic, boisterous, and social breed with a high prey drive, having been bred to hunt small rodents at places such as farms, and needs regular exercise of around one hour per day.

[2] Members of the breed typically weigh between 15 and 20 pounds (6.8 and 9.1 kg) with an average height between 10–11 inches (25–28 cm) at the withers.

[2] Westies have a deep chest, muscular limbs, a black nose, and a short closely-fitted jaw with "scissors" bite (lower canines locked in front of upper canines, upper incisors locked over lower incisors).

[citation needed] Westies have a rough outer coat that can grow to about 2 inches (5.1 cm) long[3] and a soft, dense, thick undercoat.

[citation needed] They will not typically tolerate rough handling, such as a child pulling on their ears or fur, and can frequently be both food- and toy-possessive.

They are loyal and bond with their owner but are often on the move, requiring daily exercise of at least 15–30 minutes, although an hour is the recommended minimum.

Having a typical terrier prey drive, they tend to be highly interested in toys, especially chasing balls.

[12] The disease is an autosomal recessive condition, so a puppy can only be affected by it if both of its parents are carriers of the faulty gene.

[3] About one quarter of Westies surveyed are affected by atopic dermatitis, a heritable chronic allergic skin condition.

[14] An uncommon but severe breed-specific skin condition, hyperplastic dermatosis, may affect West Highland White Terriers of any age.

The condition typically develops over one to three days, resulting in tremors of the head and limbs, ataxia, and hypermetria.

[17] Other less common conditions which appear in the breed include hydroxyglutaric aciduria, which is where elevated levels of Alpha-Hydroxyglutaric acid are in the dog's urine, blood plasma, and spinal fluid.

It can cause seizures, muscle stiffness, and ataxia, but is more commonly found in Staffordshire Bull Terriers.

It is a severe chronic hyperplastic dermatological disease that is similar to seborrhoeic dermatitis and primary seborrhoea.

Due to the fact that it is identified only in Westies, and evidence of familial involvement, it is believed to be an inherited trait.

Symptoms involve generalised and serious patches of alopecia, erythema, lichenification, hyperpigmentation, malodor, otitis externa, and pruritus.

[23][24] A 2021 British study looking at clinical records found predispositions to chronic hepatitis and hepatocellular death, caused by either toxins or acute liver failure; compared to other dogs, Westies are 3.23 times more likely to contract chronic hepatitis and 3.87 times more likely to contract hepatocelluar death.

The king ordered that a dozen of these white terriers be procured from Argyll to be presented to the Kingdom of France as a gift.

[30] The dog seemed to produce these white puppies regardless of the sire to which she was bred, and after drowning over 20 of these offspring, he came upon the theory that it was an ancient trait of the Scottish Terrier that was trying to reappear.

Flaxman is credited with classes being added to dog shows for white Scottish Terriers towards the end of the 19th century.

[31] The person most closely associated with developing the modern breed of West Highland White Terrier is Edward Donald Malcolm, 16th Laird of Poltalloch.

The first generation of Poltallochs had sandy-coloured coats, and had already developed prick ears, which is a trait seen later in the modern breed.

By the time of Malcolm's death in 1930, a stable type had appeared with prick ears, a white coat, and a short back.

Because the breed was not yet recognised independently, the championship title was not retained when the dog was reregistered as a West Highland White Terrier.

[38] As of 2010, the Westie is the third-most popular breed of terrier in the UK, with 5,361 puppies registered with the Kennel Club.