The Art and Science of Victory
Two Handed Backhand Grip
This is the simplest of all the grips. Just hold the continental grip with your right hand and place the left hand above it (closer to the head of the racquet), touching the right hand. If you get caught with an unexpected bounce or a volley hit at your body you can let go with the left hand and hit a defensive one handed shot wit the continental grip. This works on both the forehand and backhand side.The continental grip is also the best position of the right hand for a two handed backhand as the hand is in front of and above the grip in perfect opposition to the left hand which is behind and below the grip. The result is extreme leverage for hitting the topspin backhand drive.
Basics

The Two-handed backhand grip - a combination of the continental forehand grip and a comfortable left handed grip with hands as close together as possible.

Start with the forehand continental and grab the grip just above the right hand with the left. To maximize leverage and racquet head speed the hands should be as close as possible.