Albright Knot
The Albright Knot is a versatile knot that has a wide range of uses. It is only moderately easy to tie but it is suitable for joining different types of fishing line (monofilament to braided, braided to wire, etc.). It is commonly used to join the fly line to the backing line but can be used whenever you wish to join two fishing lines together.
The Albright is well suited to slide readily through the guides when a fish pulls out enough line to reach your backing. Some anglers coat the knot with a rubber-based cement to make it even smoother and more secure.