It is an age-old fact that cats and dogs don't really get along together - although there are many exceptions to the rule. Some people will say that they have kept cats and dogs together for years and have never had a problem, whilst others will admit that they have both but their furry rivals spend most of their time avoiding each other.
Dogs are pack animals and although many of their traits have been modified through selective breeding over the years, domestication cannot fully take away the instincts of nature. A dog will instinctively chase anything that moves, and the faster it moves the better - this includes people on bikes, rabbits, squirrels, sticks, toys and of course cats! Cats, on the other hand, are rather aloof and do not chase, but will pounce on anything small that moves, such as rats, mice and birds.
A dog's instinct to chase is known as its "prey drive" and this is stronger in some breeds of dogs than others - obviously the prey drive of a crossbreed would be harder to measure. Certain breeds of dogs, such as Terriers, Greyhounds and Foxhounds, have a higher prey drive than others and would be more likely to chase a cat. It is actually possible, with a great deal of training, to turn a dog's prey drive around to make the dog focus on a particular object and see this as their prey, rather than another animal - dogs used for drug detection work, such as German Shepherd dogs and Spaniels, are a good example of this.
To enable a cat and dog to get along together, you will have to introduce them to each other very slowly; putting them together straightaway and leaving them in situations where they are unsupervised, could result in disaster. You will need to begin by putting both animals in the same room together, but at opposite ends - making sure that you can restrain the dog, if necessary. Then you must reward the dog if it sits still and leaves the cat alone. Once your furry companions are comfortable with this arrangement, you can think about including some form of movement; get someone to play with the cat in the room, so that it jumps around and runs. If the dog makes any attempt to chase it, you must say: "No, stay!" very firmly. Once your dog responds well, you must reward it with a treat again. You can even use a crate for this exercise, by first putting the dog in the crate alone whilst the cat is loose in the room and then swapping them over, but don't allow either of them to show any aggression towards each other.
How well your cat and dog will get along together will depend very much on their personalities and the way you are towards them. It is always worth taking introductions slowly and trying not to do too much too soon. Hopefully, both your companions will soon learn to get along, or at least tolerate each other. You may even find that they eventually become inseparable!