The double fisherman's knot, or grapevine, joins two rope or cord ends by tying two interlocking double overhand knots. It's compact, very secure, and hard to untie after loading, which makes it the standard for tying prusik loops and cordelettes and a reliable — if stubborn — way to join rappel ropes.
A stopper knot is a backup knot tied in the tail of another knot or at the end of a rope to keep the main knot from slipping or the rope from running through a device. Climbers add a stopper to back up a tie-in figure-eight and tie stopper knots in rope ends to avoid the deadly error of rappelling off the end.
The autoblock, or French prusik, is a friction hitch wrapped around the rope and clipped back to itself, used mainly as a rappel backup. Unlike a prusik it releases easily under load and slides one-handed, so a rappeller can tend it as they descend and have it grab the rope if they let go of the brake.
The klemheist is a friction hitch, similar to a prusik, tied with cord or webbing around a rope so it grips when loaded and slides when relaxed. Unlike the prusik it is directional — gripping only when pulled one way — and it slides more easily, making it useful for ascending a rope and as a rappel backup.
The flat overhand bend, often nicknamed the European Death Knot (EDK) despite being safe when tied correctly, joins two rappel ropes with a simple overhand knot in both strands. Its flat profile lets it slide over edges and roofs without snagging, making it the preferred knot for joining rappel ropes — provided the tails are left long.
A figure eight on a bight is a figure-eight knot tied in a loop (bight) of rope rather than the end, creating a strong, easy-to-inspect loop anywhere along the rope. Climbers use it to clip into anchors, attach to the middle of a rope, and build master points, sharing the figure-eight's strength and visibility.
The alpine butterfly is a knot that puts a secure, load-bearing loop in the middle of a rope without needing the ends. Climbers use it to isolate a damaged section of rope, to tie into the middle of a rope on a glacier team, and to clip a third climber into the system. It can be loaded in any direction.
The water knot, or ring bend, is the standard knot for joining the ends of flat webbing into a sling or runner. It's a retraced overhand knot that holds well in webbing, where many other knots slip. The tails must be left long and the knot checked regularly, since water knots can slowly creep loose over time.
The bowline is a knot that forms a fixed loop at the end of a rope, used by some climbers as an alternative tie-in and to attach the rope to anchors or trees. Its main advantage over the figure-eight is that it unties easily even after heavy loading, but it must be backed up, since an unsecured bowline can shake loose.
Climbing knots are the small set of knots, hitches, and bends that climbers rely on to tie into the rope, build anchors, rappel, and perform rescues. A handful do almost everything — the figure-eight to tie in, the clove and munter hitches at the anchor, and friction hitches like the prusik for ascending and backups.