A hard shoulder or simply shoulder is a reserved area alongside the verge of a road or motorway. It is usually slightly smaller than the width of a full traffic lane. In the United Kingdom and Ireland, the hard shoulder is demarcated by road markings in the form of a single dashed yellow line, possibly with the addition of cat's eyes. In the United States, the right-hand shoulder is separated by a solid white line, and the left-hand shoulder (if the road is a divided highway) is separated from the main road by a solid yellow line.

Generally the hard shoulder is kept clear of all traffic. In the event of an emergency or breakdown, a motorist can pull into the hard shoulder. Thus the hard shoulder offers some element of safety for stalled vehicles. A hard shoulder also allows some extra flexibility should a motorist need to take evasive action, it is a buffer area between the main thoroughfare and the edge of the road. This is particularly true for two-lane roads; for example, slower vehicles may drift into the hard shoulder to allow more room for those who wish to overtake.

It is extremely unsafe, as well as illegal, to abuse the hard shoulder by 'undertaking' (an apt term); passing out vehicles that are nearer the centre of the road. (Some roads and expressways have a hard shoulder that is of such a narrow width that 'undertaking' is impossible.) However in some places buses are allowed to pass on the shoulder when traffic jams block the main road, and emergency vehicles have the same right.

In some jurisdictions police and other emergency vehicles are allowed to temporarily allowed to use the hard shoulder to get by traffic; this is the case in mainland China and Taiwan.