A rowlock (UK: ), sometimes spur (due to the similarity in shape and size), oarlock (American English) or gate, is a brace that attaches an oar to a boat. When a boat is rowed, the rowlock acts as a fulcrum for the oar.

On ordinary rowing craft, the rowlocks are attached to the gunwales. In the sport of rowing, the rowlocks are attached to outriggers (often just called "riggers"), which project from the boat and provide greater leverage. In sport rowing, the rowlocks are normally U-shaped and attached to a vertical pin which allows the rowlock to pivot around the pin during the rowing stroke. They additionally have a locking mechanism (properly known as "the gate") across the top of the "U" to prevent the oar from unintentionally popping out of the rowlock.

Originally, rowlocks were two wooden posts or thole pins that the shaft of the oar nestled between. Single thole pins may be used when the oars have holes cut into the loom, which then sits over/around the thole pin.