On a sailboat, a backstay is a piece of standing rigging which keeps a mast from falling forewards. It is attached at the very top of the mast. The other end of the backstay is attached to the stern of the vessel. On modern yachts, the backstay is often adjustable. As the wind builds up, more tension is applied to the backstay, depowering the sails and making the boat easier to handle.

Contrast with forestay and shrouds.