Cared for properly, good boots will last a long time - often five to ten years, depending on how hard you and the terrain are on them.
Knowing boot anatomy and available boot features area big part of the boot buying process.
Full Grain is the outermost part of the cow's hide; it is the stiffest, most waterproof type of leather. It is sometimes turned inside-out (rough-out) so the smooth, outer layer won't get nicked or scratched.
The The Upper part of the boot should have as few seams as possible. A one-piece upper is more water resistant.
A Gusset is a thin piece of flexible leather sewn to both the tongue and the upper. It keeps out water and stones. A "bellows" tongue has wide gussets, allowing it to open further so it is easy to put on. Some boots have two "overlapping" tongues, each connected to one side.
The The Back-Stay is a strip of leather sewn over the back seam. If it gets torn or chafed, it is almost impossible to replace. For that reason, it should be as narrow as possible.
A Welt is the stitch which connects the upper sole. A Norwegian welt is double-stitched, strong and stiff. Other welts are not as strong but allow more flexibility .
A Rand is a wide rubber strip protecting the stitching that holds the upper to the sole.
The Sole has three parts: a padded "footbed" just below your foot, an "insole" below the footbed and an "outsole" on the bottom. The insole can be soft and flexible for light hiking, or it can be stiffened with a half- or full-length "shank" (sheet) of plastic or steel for added support. The sole is made of rubber (Vibram is a type of stiff hard rubber) with a "lug" pattern designed for gripping the path. Deep lugs are best for steep rugged terrain, while shallow lug patterns are lighter and more flexible.
Consider the following when your're in the market for hiking boots:
Leather or Lightweight? Leather is strong, tough, durable and heavy. Great for serious mountaineering. Lightweights are made of plastics, nylon and other synthetics. They literally take a burden off your feet. Sturdy, flexible, and comfortable, they are perfect for hiking and most backpacking.
Soles. The thicker the Vibram rubber sole and the deeper the treads or "lugs," the greater the traction but the heavier the boot. Likewise, the stiffer the "mid-sole" layer above the rubber sole, the stronger but less pliable and comfortable the boot. Day hikers don't need steel/plastic mid-soles; mountaineers do.
Welts. Welts are stitching systems that join boot to sole. The better the welts, the stronger the join. Hence welts make shoes that are more water-tight, more durable, though perhaps less flexible. Lighter shoes use bonding-cement joins.
Aside from the appropriateness of the boot (you don't want technical mountaineering boots, unless of course you are a technical mountaineer) and the cost, the all-important consideration is size. Get it right. You and your hiking mates will regret it if you don't. Seek out a reputable store and an experienced salesperson to find the best fit. Wear the same socks (or inner and outer socks) you'll be wearing on the trail.