As one of the primary contact points on the bike and as the place where all of the power is applied, shoes are an absolutely crucial piece of mountain bike gear. Mountain bike shoes come in a variety of types, although the two main versions are clipless shoes and flat pedal shoes.
Clipless shoes feature a spot where a metal cleat can be bolted in place, whether it's an SPD cleat, a Crankbrothers cleat, or a Time cleat. Good cross country shoes are generally as light and as stiff as possible, and feature Velcro straps and a ratchet strap for the closure (although some newer shoes feature a Boa closure). All mountain and enduro shoes generally provide more lugs on the soles of the shoe for extra traction when hiking.
Flat pedal shoes feature a flat bottom made of sticky rubber that is designed to stick to the sharp metal pins found on flat pedals. Freeride and downhill mountain bikers generally use these shoes, although flat pedals have been gaining more acceptance in recent years in all disciplines, including cross country. Popular flat pedal shoe brands include Five Ten and Teva.
Some mountain bike shoes seek to break convention by including a flat pedal design with an optional cleat mount, which allows the rider to choose how they would like to use their shoes.