In the most ideal of winter conditions–that is, no ice, no snow, no puddles, and no extreme cold – you can wear any boot as a winter boot, provided you have thick enough socks. But in general, winter-specific boots are made for those non-ideal conditions. They always have some insulation for extra warmth, should be waterproof (all the ones we've selected are waterproof or water-resistant), and should have some kind of outsole (bottom) designed for traction in wet and slippery conditions. Beyond that, some are more focused on style and versatility, while others keep your feet warm in borderline arctic conditions. They may also run slightly larger than a standard street shoe size, as it's anticipated you'll be wearing thicker-than-average socks. Remember that getting a boot with too much insulation or one rated for conditions far colder than your typical environment can be a downside. Too much warmth actually is a bad thing, as it can cause your foot to sweat, and when the moisture inside your sock and boot cools down, your feet will get very cold. That's why a breathable boot is a good thing, though it may sound counter-intuitive for winter wear.