A passing lane (North American English), overtaking lane (English outside North America) is a lane on a multi-lane highway or motorway closest to the median of the road (the central reservation) used for passing vehicles in other lanes. (North American usage also calls the higher-speed lane nearest the median the "inside lane" but in the United Kingdom this is the "outside lane".) Countries with right-hand traffic put the passing lane on the left; those with left-hand traffic put the passing lane on the right. Motorways typically have passing lanes along their entire length, but other roads might only have passing lanes for certain segments, depending on design specifications typically related to available space, funding, and traffic levels. A 2+1 road alternates the passing lane between directions every few kilometers.

The passing lane is commonly referred to as the fast lane, and the lane closest to the shoulder the slow lane. Some jurisdictions, particularly on limited-access roads, ban passing-lane driving while not overtaking another vehicle; others merely require slower cars to yield to quicker traffic by shifting to slower lanes, or have no limitations.

On roads with only one lane in a given direction, overtaking is accomplished by briefly pulling into oncoming traffic. This is often prohibited by "no passing" signs and road markings on lengths of road where a hill or a curving road limit sight distances, and some jurisdictions ban this entirely. So-called suicide lanes provide a shared third center lane for passing in both directions, with the expectation that drivers will check for oncoming traffic before entering.

In modern traffic planning, passing lanes on freeways are usually designed for through/express traffic, while the lanes furthest from the median of the road have entry/exit ramps. However due to routing constraints, some freeways may have ramps exiting from the passing lane; these are known as "left exits" in North America.