The Bullmastiff is a large breed of dog that can weigh anywhere from 100 to 130 pounds or more and stand up to 27 inches tall. They originated from a cross between the Mastiff and the Bulldog. Breeders wanted to mix the courage of the Bulldog with the guarding ability of the Mastiff to create a dog that was very quick when it needed to be. The result was the Bullmastiff.

Due to their size, they are excellent working dogs. They were originally given the nickname of "gamekeeper's nightdog" in Britain because of their work at alerting the gamekeepers when there were poachers coming. If their masters were involved in a fight with the poachers, the Bullmastiff would help. They were trained to attack on command, knock the person down and hold him down. The dog would know he was not to attack the poacher, but just hold him down.

Today the Bullmastiff is very successfully used as a guard dog in many homes and businesses. Because of their great strength, size, and endurance, they are able to overtake an intruder without having to actually hurt them. Their one fault is being stubborn, which makes obedience training a little difficult, but their protectiveness of their family makes up for that and makes them great guard dogs. They seldom bark but when they do bark, it is a deep sound that alerts everyone near them. They were bred to guard so a lot of it comes naturally to them. The owner or trainer has the task of deciding what limitations they want put on their "guard duty".

Due to their guarding ability and extreme intelligence, they are used as a police and army dog to help these services in their line of work. They are the most requested dog for many of these services. The Diamond Society in South Africa uses the Bullmastiff as their watchdog. The main reason why many choose the Bullmastiff as their watchdog or guard dog is because they have the courage, strength, and endurance to guard the place and overtake an intruder without actually biting them, thus preventing any possible lawsuits.

Although the Bullmastiff is generally used as a guard dog due to their massive size, many owners realize what great working dogs they are and extend their training to many working titles. Schutzhund is a title that owners often find very challenging for a Bullmastiff. Schutzhund is a competition sport that has three different categories: basic obedience, tracking, and protection. For a Bullmastiff to be able to successfully complete Schutzhund training would be a real definition of how intelligent and hard working the Bullmastiff really is. The amazing quality of the Bullmastiff is that there is very little training required for them to become excellent watchdogs and guard dogs. From the time they are little, the guarding instinct is inside them.