Guard rail or guardrail, sometimes referred to as guide rail or railing, is a system designed to keep people or vehicles from (in most cases unintentionally) straying into dangerous or off-limits areas. A handrail is less restrictive than a guard rail and provides both support and the protective limitation of a boundary.

Public safety

Most public spaces are fitted with guard rails as a means of protection against accidental falls. Any abrupt change in elevation where the higher portion is accessible makes a fall possible. Due to this responsibility and liability, rails are placed to protect people using the premises. Guardrails are generally required by code where there is a drop of 30" or more.

Examples of this are both architectural and environmental. Environmental guard rails are placed along hiking trails where adjacent terrain is steep. Railings may also be located at scenic overlooks.

Guard rails in buildings are numerous, and are required by building codes in many circumstances. Guard rails along stairways are common, and catwalks and balconies are also lined with them.

Building codes also require that no opening in a guard be of a size such that a 4" sphere may pass. There are three exceptions according to the 2003 International Building Code Section 1012.3 which allow openings to not exceed 8" or 21" depending on occupancy groups or special areas.

An architect who was famous for creative use of handrails for social stability was Alvar Aalto. The guard rails of an observation tower such as the Space Needle or Eiffel Tower become exaggerated to the point of becoming a fence or cage. This is also done on bridges and overpasses to prevent accidents and suicides.