Gunter rig is a configuration of sail and spars used in sailing. It is a fore and aft sail set abaft (behind) the mast. The lower half of the luff (front) of the sail is attached to the mast, and the upper half is fastened to a spar which is approximately vertical and reaches above the top of the mast. This spar is called a "yard", but it is common for some to confuse it with a "gaff" (as in gaff rig).^: 38 The overall shape of a gunter sail is roughly triangular, so having a superficial resemblance to Bermuda rig.

A gunter sail may also be called a "gunter lug" - a name which suggests developmental origins from increasing the angle of a high peaked standing lug.^: 91 Gunter sails are sometimes described as "sliding gunter".

Gunter rig is generally used in small sailing craft. One important advantage is that the shorter mast used with this rig usually fits within the hull when unstepped, together with the boom and yard. This is helpful for a dinghy that is towed behind a car, stored in a garage, or used as a tender for a larger boat. The performance to windward comes close to that of Bermuda rig.^{: 38 : 91} Gunter rig can be found in a few working craft, but the majority of uses are in pleasure craft.

There are many variations of gunter rig: the most fundamental of which include whether the sail is hoisted with one or two halyards, and the ease with which reefs can be taken in.