A Prusik ( PRUSS-ik) is a friction hitch or knot used to attach a loop of cord around a rope, applied in climbing, canyoneering, mountaineering, caving, rope rescue, ziplining, and by arborists. The term Prusik is a name for both the loops of cord used to tie the hitch and the hitch itself, and the verb is "to prusik" (using a Prusik to ascend). More casually, the term is used for any friction hitch or device that can grab a rope (see autoblock). Due to the pronunciation, the word is often misspelled Prussik, Prussick, or Prussic.

The Prusik hitch is named after its putative inventor, Austrian mountaineer Karl Prusik. It was shown in a 1931 Austrian mountaineering manual for rope ascending. It was used on several mountaineering routes of the era to ascend the final summit, where a rope could be thrown over the top and anchored so that climbers could attain the summit by prusiking up the other side of the rope.

A Prusik made from cord does little or no damage to the rope it is attached to, whereas some mechanical ascenders (not Prusiks) can cause damage from normal use, and especially if the device slips during climbing or is heavily loaded or shock loaded.