A spire is a tapering conical or pyramidal structure on the top of a building, particularly a church tower. Etymologically, the word is derived from the Old English word spir, meaning a sprout, shoot, or stalk of grass.

Symbolically, spires have two functions. The first is to proclaim a martial power of religion. A spire, with its reminiscence of the spear point, gives the impression of strength. The second is to reach up toward the skies. The celestial and hopeful gesture of the spire is one reason for its association with religious buildings. A spire on a church or cathedral is not just a symbol of piety, but is often seen as a symbol of the wealth and prestige of the order, or patron who commissioned the building.

As an architectural ornament, spires are most consistently found on Christian churches, where they replace the steeple. Although any denomination may choose to use a spire instead of a steeple, the lack of a cross on the structure is more common in Roman Catholic and other pre-Reformation churches. The battlements of cathedrals featured multiple spires in the Gothic style (in imitation of the secular military fortress).

Spires also occur commonly and notably as solo structures, in the way that obelisks are used. The Modernist movements of the 20th century began to build office towers in the form of free-standing spires. Some famous buildings, such as the Space Needle in Seattle, Washington, use the spire as a testimony of civic power and hope; this example also references Seattle's participation in aerospace. The 1,776-foot (541-m) One World Trade Center building at Ground Zero in New York City is built with a spire, the height of which (being a permanent structure and not just an antenna) puts the building over the mark for the tallest building in the United States. Without the spire, the Willis Tower would still hold the title for tallest building in the US.