In sailing, a gaff is the upper spar used to control a fore-and-aft sail set aft of the mast, such as a mainsail.

Now largely obsolete, gaff rig was once the normal rig on classic schooners and all other sailing ships using fore-and-aft rigging, and also on sailing dingies.

A gaff may be raised either by one or two halyards. On larger vessels, the peak halyard raises the end of the gaff further from the mast, and hauls the gaff towards the mast when the sail is set, while the main or throat halyard raises the end of the gaff closer to the mast, and bears most of the weight of the sail and also the luff tension when the sail is set.

On smaller boats, a single halyard raises the gaff, an arrangement known as gunter rig after the wire gunter that runs along the top of the gaff, and along which the end of the halyard runs by means of a block.

In fishing, a gaff is a pole with a hook on the end that is used to stab a large fish and then lift the fish into the boat. Ideally, the hook is placed under the backbone. Gaffs are used when the weight of the fish exceeds the breaking point of the fishing line or the fishing pole, but cannot of course be used if it is intended to release the fish unharmed after capture.