The Reef Knot—also known as the Square Knot—is as simple as tying your shoes. In fact, it is tying your shoes.
Step 1: Hold rope Hold one end of the rope in your left hand and the other end in your right hand.
Step 2: Cross ends Cross the end of the rope in your left hand over the end in your right hand to form an "X."
Step 3: Entwine ends Bring the end of rope in your left hand down behind the end in your right hand, then back up, so that the two ends are entwined—the left-hand rope is now in your right hand and vice-versa.
Step 4: Form another "X" Use your right hand to pass the same end back over the end now in your left hand, forming another "X."
Step 5: Pull end through loop Bring that end down behind the other end again, and continue pulling it through the loop that forms.
TIP: This knot can also be tied using two separate ropes, joining them in a "hitch."
Step 6: Pull ends Pull the two ends to a symmetrical length, and you've got a perfect square Reef Knot on your hands.
FACT: A helpful mnemonic device to tie this knot: Left over right, right over left.