Has your car ever felt like it has a mind of its own? As if it wants to make right- or left-hand turns while driving or braking?
If so, this could indicate a problem with the braking system. The cause of this pulling might be a stuck caliper. Because such a scenario would cause friction on one wheel and not the others, your car can pull to the side where the caliper is stuck.
Two other brake-related scenarios that could cause a car to pull would be a collapsed brake hose that would cause your calipers to move unevenly when applying the brakes, or uneven brake pads, which would also apply different amounts of pressure to different wheels.
Pulling, however, doesn't always indicate a problem with the brakes. The cause could also come from unevenly inflated or worn tires, poor alignment or a problem with your vehicle's suspension. This is why, if your car begins to pull, you'll want to pull it into the nearest mechanic's shop for a full workup.