You can go a long way toward discovering what you need in a running shoe by looking at your feet. There are three basic foot types, each based on the height of your arches. The quickest and easiest way to determine your foot type is by taking the "wet test," below.
1) Pour a thin layer of water into a shallow pan
2) Wet the sole of your foot.
3) Step onto a shopping bag or a blank piece of heavy paper.
4) Step off and look down
Observe the shape of your foot and match it with one of the foot types at the bottom of the page. Although other variables (such as your weight, biomechanics, weekly mileage, and fit preferences) come into play, knowing your foot type is the first step toward finding the right shoe for you.
Normal (medium) Arch
If you see about half of your arch, you have the most common foot type and are considered a normal pronator. Contrary to popular belief, pronation is a good thing. When the arch collapses inward, this "pronation" absorbs shock. As a normal pronator, you can wear just about any shoe, but may be best suited to a stability shoe that provides moderate arch support (or medial stability). Lightweight runners with normal arches may prefer neutral-cushioned shoes without any added support, or even a performance-training shoe that offers some support but less heft, for a faster feel.
Flat (low) Arch
If you see almost your entire footprint, you have a flat foot, which means you're probably an overpronator. That is, a micro-second after footstrike, your arch collapses inward too much, resulting in excessive foot motion and increasing your risk of injuries. You need either stability shoes, which employ devices such as dual-density midsoles and supportive "posts" to reduce pronation and are best for mild to moderate overpronators, or motion-control shoes, which have firmer support devices and are best for severe overpronators, as well as tall, heavy (over 165 pounds), or bow-legged runners.
High Arch
If you see just your heel, the ball of your foot, and a thin line on the outside of your foot, you have a high arch, the least common foot type. This means you're likely an underpronator, or supinator, which can result in too much shock traveling up your legs, since your arch doesn't collapse enough to absorb it. Underpronators are best suited to neutral-cushioned shoes because they need a softer midsole to encourage pronation. It's vital that an underpronator's shoes have no added stability devices to reduce or control pronation, the way a stability or motion-control shoe would.