At first glance, Shelties and Collies look almost the same. As puppies, they might even look identical but as they reach adulthood, the size difference becomes more obvious.

The reason for their striking similarity is because earlier Shelties were crossbred with Collies. This was in order to refine the diminutive herding dog from the Islands of Shetland. Despite this fact, the quantity of the Collie breed in Shetland sheepdogs is small. The two breeds were raised separately which fostered independent developments. The Collie progressed in Scotland while the Sheltie evolved in the Shetland Islands. Marked differences can be found in each of the breed’s history, size, physical characteristics and temperament.

Compared to the Sheltie, the Collie has been present in history books since the 17th century. 1655 wooden carvings show pictures of dogs that look identical to today’s Collies. These herding dogs originated from Scotland. Initially, they were named "Colleydogs" because of the duties they performed for their owners. Many farmers raised these puppies to later herd the sheep in the country’s highlands. A colley is a black mask found on the sheep.

In the Shetland Islands, an antique copper etching dating back to 1840 contained pictures of a small dog. This was the first evidence of the Shetland sheepdog’s heritage. Shelties also herded sheep but unlike its counterpart, the Collie, Shelties were used to keep sheep away from "toons" or small villages. Collies herded sheep in the mountains, while Shelties herded sheep away from the crops. Sheep were notorious for eating what farmer’s have planted. For this reason, Shelties were originally known as "Toonie Dogs".

Again, there is a resemblance in the coats but one can still tell them apart. The Collie’s original colors were black and white, which no longer exists. Today’s breed can come in blue merle, sable and tricolor. Collies used to be bred with the Gordon Setter which is responsible for the tricolor puppies. Coats of this breed can be long or short. The short-coated variety makes it look naked compared to its long-coated cousins.

The Sheltie’s original shades were tan and white. This also no longer exists. Today’s Shelties come in black and white, sable, tricolor and blue merle. Tales of how, a yacht that was visiting the islands left a King Charles Spaniel. This became the source of tricolor puppies. The gene could be traced back to that Spaniel. The Shetland Sheepdog should not have a short coat. It must have a harsh upper coat, in addition to the thick undercoat. Collies and Shelties both have rich coats. In the areas surrounding the head, chest and tail, the fur is especially thicker.

Probably the most obvious difference between the two breeds is the size. A Sheltie’s height ranges between 35 and 39cm, depending on the sex. These dogs weigh 7-12 kg. Collies are much bigger. Their height range is 51-61cm at the shoulders. Ideally, a Collie’s weight should be within 18-30kg.

Both dogs are known for their alertness, willingness to please their owners and for being active. Shelties, however, are a bit livelier compared to Collies.