The Fisherman's Knot is a convenient method of attaching two ropes together. Although this knot will work to attach monofilament fishing line, stronger knots are available (such as the clinch knot). Regardless, it remains a quick and easy method to connect rope with a clean symmetrical finish. Note: this knot does have the potential to slide.
Align the two ends of your rope parallel to each other and make alternating overhand knots.
Tighten the knots and pull the ends apart such that the knots abut tightly against each other.