Bowline

The Bowline (BOH'-LIN) is considered the boaters' prime knot. A commonly used knot to tie a loop in the end of a rope. It has the advantage of not jamming, compared to some other loop forming knots (for example when using an overhand knot on a large bight to form a loop). The bowline is used to tie sheets and halyards (control lines) to sails, to temporarily tie a rode (anchorline) to an anchor, or, using one knot on each line, tie together 2 lines of different diameters. Two bowlines tied close together can be used to make an emergency bowswain's chair to go up the mast or bring an injured person aboard.

The benefits of the bowline are in its loop that will not slip, and in its ability to be untied after being exposed to a strain.
Form a small loop (the direction is important), and pass the free end of the knot up through the loop, around behind the standing part of the rope, and back down through the loop.
A chant used by many to remember this knot is "The rabbit comes out of the hole, round the tree, and back down the hole again", where the hole is the small loop, and the rabbit is the running end of the rope.
In the same way that a Left Handed Sheet bend is a Sheet bend that has the running end of the rope coming out of the wrong side of the knot, a cowboy bowline is a bowline that also has the running end of the rope coming out of the wrong side of the knot. It suffers the same problems as the left handed sheet bend.

Tip. Don't be afraid to use this knot to form a loop of any size in rope.
Tip. To quickly identify if you have tied the Bowline normal or left handed, check to see that the running end exits the knot on the inside of the loop.
Tip. For added security, finish the knot with a stop knot such as a Figure of Eight knot to remove any possibility of the Bowline slipping.
Tip. If you use this knot in a man carrying situation - perhaps a rescue where a harness is unavailable - then you MUST use a stop knot as mentioned above.
Bowline Knot Lore
At sea, the bow line was a rope used to hold the weather leech of a square sail forward closer to the wind, to prevent it from being taken aback (that is, unintentionally blown inside out, impeding the ship's progress). So the knot that secured it was literally a bow line knot, but it has since become diminished and its pronunciation altered.