Pet dogs were released with the Summoning skill on 15 January 2008. It only requires level 4 (for this is the minimum Summoning level after the quest Wolf Whistle) Summoning, and can be used throughout the Runescape world. Players may only own one dog or puppy at a time (for members with at least level 37 Construction, adult dogs can be kept in the Menagerie room of their Player-owned House, which allows purchase of an additional puppy - though this may be a glitch.) Breeds include a Labrador, Dalmatian, Greyhound, Sheepdog, Terrier and a Bulldog. Your pet dog grows hungry over periods of time without feeding. It grows physically over time (when you take it out). Feeding your dog raw meats such as raw beef, raw bear meat, raw rat meat, and raw beast meat (raw yak meat, bird meat or fish of any kind won't be eaten) will cure its hunger by resetting its hunger level to 0%. Feeding your dog bones will not decrease its hunger level. Also note that there is no benefit in feeding your dog except to stop the warning messages about the dog being hungry. The pet dog will not run away even at 100% hunger rate but it will stop growing.
With a Summoning level of 12, you can understand what the dog says. This will make it say various things instead of "Yippity Yap!"
To get your dog to follow you, you will need to right-click and select the Walk with option. To pick it back up, you need to either left-click, or right-click and select the pick-up option.
Pet dogs (like other pets) provide the player with no benefits.
For more information about specific dogs, see these articles: