The connection between you and your whip is very important. One thing many whip users do is evaluate another whip user by how they hold the whip. It speaks of knowledge and experience and what their influences and style of whip use are.
There are a few ways to grip a whip. The most modern is the ball and socket, favored by a lot of top men. TOP men. The whip is held by the turkshead knot in a loose, swiveling grip. This allows a squeeze on the handle to add energy to the whip and facilitate the forming of a rolling loop. The "V" of the hand between the index and forefinger is used for alignment purposes. Wrapping is delicate and accuracy superb.

Then there a few variations on this. Using the index finger for alignment and a bit more leverage. Picked this one up from Kendall Wells.

Another variation is the use of the thumb as opposed to the index finger.

The grips above account for the majority of grips in use today. Because it works and allows you to do less with more. Even Indiana Jones used the ball and socket grip in The Kingdom of the Crystal Skull, thanks to weeks of intensive training under whip coach Anthony DeLongis.
But in examining images in  "The Complete Making of Indiana Jones" I came across time and time again what I've begun calling The Harrison Grip. From Raiders to Crusade this is the grip Indiana Jones used. Harrison has admitted that his whip work in the movies is a result of a few lessons and a lot of self teaching.
We had a guy come to my house for a couple of lessons with the bullwhip in the beginning, I think it was three or four lessons. Then it was up to me to practice with it and get it right. If anybody could explain it in words, I'm sure it would be a lot easier to do. It's a combination of relaxation while snapping the wrist at the proper time. It's really all a matter of timing. Once you've learned how to do it, you remember the basics so you're not lashing yourself with the whip. I usually practice with several bullwhips on posts and trees. It's not an easy thing to learn, though. I did take the bullwhip out a few weeks before I started on Indy III and loosened up a bit."
—Harrison Ford (Thanks to Indygear.com)

Notice the position of the hand, on the handle. In some images Harrison is using the thumb for alignment, in others he's not. This creates more a club then a whip, resulting in a vicious slashing strike and a loud crack. Wrapping is not delicate but brutal, ideal for disarming Thugee Warriors or back stabbing Central American lackeys. This is a grip to take fingers off and cut to the bone. With the leverage gained by making the whip part of your arm, multiple cracking is possible but it's far from elegant. It is can also create a need for more follow through, not pointing the handle but hacking through your target. And for any Indiana Jones fan who wants to learn how to use a whip just like our hero, a must. If only for demonstration purposes and our own self interest. It's amazing how far whip work has come since Indiana Jones first appeared on screen. Just look at the grip!