Overgrips are literally just those, you put them on top of your existing grip to either save replacing the original grip. They are useful to get a better grip or feel of your tennis racket, or to keep the sweat at bay. For the latter reason, we recommend changing your overgrip regularly for hygienic reasons, and if you play a lot it may be worth going for the larger multi-packs. The only thing you need to watch out for is the different textures. There are sticky grips, tacky grips and even dry grips which have a texture like blotting paper to absorb the sweat. Roger Federer uses the best selling sticky overgrip, the Wilson Pro Overgrip. Rafa Nadal uses the Babolat VS Original overgrips. The best selling dry overgrip is the Tournagrip Original.