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Wooden ties are used on many traditional railways. In the background is a track with concrete ties.
A railroad tie/railway tie/crosstie (North America), or railway sleeper (UK and Australia) is a rectangular support for the rails in railroad tracks. Generally laid perpendicular to the rails, ties transfer loads to the track ballast and subgrade, hold the rails upright, and keep them spaced to the correct gauge.

Railroad ties were traditionally made of wood, but pre-stressed concrete is now widely used, especially in Europe and Asia. Steel ties are common on secondary lines in the UK; plastic composite ties are also employed, although far less than wood or concrete. As of January 2008, the approximate market share in North America for traditional and wood ties was 91.5%, the remainder being concrete, steel, azobé (red ironwood) and plastic composite.[1]

Coarse aggregate is the standard material for track ballast, which provides drainage and resilience. On lines with lower speeds and axle-weights, sand, gravel, and even coal ash from the fires of steam locomotives have been used.

Up to 3000 ties are used per mile of railroad track in the US, 2640 per mile (30 per 60 ft rail) on main lines in the UK. Rails in the US may be fastened to the tie by a railroad spike; iron/steel baseplates screwed to the tie and secured to the rail by a proprietary fastening system such as a Vossloh or Pandrol are commonly used in Europe.