Tracheids are long tubular cells in the wooden parts of plants. They are one of the two types of xylem plant tissue (the other being vessel elements). Tracheids have two major functions, particularly in structural support and the conduction of water and soil minerals collected by the roots to the upper parts of the plants. This transport does not happen in reverse.

Tracheids are located in the xylem, along with wooden vessel elements. They occur as rigid fiber bundles throughout the plant to provide resource transportation to leaves and peripheral sections of the plant.

The presence of tracheids (and other water-conducting cells) is the defining characteristic of vascular plants to differentiate them from non-vascular plants. In seedless vascular plants and gymnosperms, they are the most important water-conducting vessels. In angiosperms, they serve a lesser role as wood vessels have largely taken over the function of conducting water.