In many countries it is 'recommended' but not actually a law. Where I live in western BC, Canada, that's the case. There are even large roadside signs asking slower drivers to keep to the right. -It doesn't seem to stop many slower drivers just moseying along in the left (Fast) lane as if they are the only road users.
In New Jersey it is a Law. Left lane is actually for passing.
When you are in a country that drives on the right, then generally you should drive in the right lane; the left lane is for passing. When you are in a country that drives on the left, then generally you should drive in the left lane; the right hand lane is for passing only.
Slow traffic keep right sign
In general, you should keep to the right at all times unless passing, and you definitely should remain in the right lane when traveling below the speed limit.
Because everyone is trying to pass the slower moving traffic and most highways are posted with the sign, "Slower traffic keep right" or the left lane (passing) is marked "Through Traffic".
The slower traffic keep right sign means that drivers who choose to drive less than the speed limit should stay in the right-hand lane. For example, 18-wheelers going up a hill often experience decreased speed because of the weight they haul. Unless passing an even slower vehicle, the slower truckers need to stay in the right-hand lane. Vehicles driving significantly below posted speed limits should also use their flashers until they are able to match the posted speed limit.
The slower traffic keep right sign means that drivers who choose to drive less than the speed limit should stay in the right-hand lane. For example, 18-wheelers going up a hill often experience decreased speed because of the weight they haul. Unless passing an even slower vehicle, the slower truckers need to stay in the right-hand lane. Vehicles driving significantly below posted speed limits should also use their flashers until they are able to match the posted speed limit.
The slower traffic keep right sign means that drivers who choose to drive less than the speed limit should stay in the right-hand lane. For example, 18-wheelers going up a hill often experience decreased speed because of the weight they haul. Unless passing an even slower vehicle, the slower truckers need to stay in the right-hand lane. Vehicles driving significantly below posted speed limits should also use their flashers until they are able to match the posted speed limit.
(in the US) even if not posted, the generally understood(even if unwritten) rule applies in most things - slower traffic (i.e.: pedestrians) keep right - faster traffic (i.e.: bikes) pass on the left.
If you are a normal car you should use the middle lane unless you are turning of.
Drivers intending to stay on the highway/freeway should stay in the right lane or the lane designated as a through-lane. The only times you should move left is to allow vehicles to merge from a right side on ramp (and move back to the right lane as soon as you can), or to pass slower traffic already in the right lane (then move back to the right lane when it is safe to do so). If a freeway provides a "slower" lane and you drive slower than the maximum speed allowed, you should use the slower lane. But never hog the passing lane just to keep driving in it; move over and let faster traffic pass you.
When driving on a four lane highway or freeway you should use the right hand land or 'thru lane' except when passing. If the right hand lane is designated for slower traffic or for exiting traffic, you'd use the lane to the left of it.
When you are in a country that drives on the right, then generally you should drive in the right lane; the left lane is for passing. When you are in a country that drives on the left, then generally you should drive in the left lane; the right hand lane is for passing only.