The bowline ( or ) is an ancient and simple knot used to form a fixed loop at the end of a rope. It has the virtues of being both easy to tie and untie; most notably, it is easy to untie after being subjected to a load. The bowline is sometimes referred to as King of the knots because of its importance. Along with the sheet bend and the clove hitch, the bowline is often considered one of the most essential knots.

The common bowline shares some structural similarity with the sheet bend. Virtually all end-to-end joining knots (i.e., bends) have a corresponding loop knot.

Although the bowline is generally considered a reliable knot, its main deficiencies are a tendency to work loose when not under load (or under cyclic loading), to slip when pulled sideways, and the bight portion of the knot to capsize in certain circumstances. To address these shortcomings, a number of more secure variations of the bowline have been developed for use in safety-critical applications, or by securing the knot with an overhand knot backup.