In response to a question posed in Der_Pacemaker's Running Forum on pronation, I posted the following reply, republished here so that others can also be informed.
Anyway, pronation actually is normal. The usual footplant happens with your eg. right foot landing in the slightly outer region (lateral side) and then rolling slightly inward before toeing off.
The inward roll is so that your body can cushion your landing and it's perfectly natural. It's when your foot lands and rolls excessively inward that you're OVERpronating. This tends to happen to larger guys lacking supportive footwear. Weakness in the leg/foot area is the other cause. Remedies include wearing orthotics (supportive shoe inserts) or getting shoes with some medial (inner side) support or called medial posts. Overpronators typically have flat feet (collapsed arches).
Shoe companies market their support devices using many names:
Asics - Duomax which works with their Trusstic and IGS Systems
Adidas - 3D Torsion
Nike - Footbridge
Mizuno - Wave Technology
New Balance - Rollbar with Stability Web and ENCAP
Typically shoes with support can be worn by everyone, though efficient and neutral runners can do away with the additional weight and bulk. A clear indication that the shoe is a support shoe would be the midsole in the medial area is slightly harder (higher density) or of different colour/shade. Yes, they're not for cosmetic reasons solely (pun intended)!
Conversely if you're an UNDERpronator, your feet don't recovers from the initial footplant and instead roles on the outside. An underpronator aka supinator's feet has high arch and is not flexible (hence not rolling in). These guys need shoes with cushioning.
Hope my little take on the subject helps. Need more info? Post it up on the forum!