Weather can be unpredictable at high altitude. Days may be balmy and bright, while nighttime temperatures dip below freezing. The wind can be punishing, especially when you get above the tree line where shelter is hard to find, and rain or snow squalls can strike unexpectedly.
So, in addition to all the usual things one must consider when choosing a sleeping bag or tent (weight, price, capacity, seasonal rating), you also need to take the unpredictable conditions at high altitude into consideration.
When it comes to tents, mountaineering and expedition varieties are best-suited to the rigors of high-altitude camping. Look for a tent with stakes and guy lines sturdy enough to anchor it in punishing wind and bad weather conditions. The downside of these tents is that they are made of heavier fabrics and use more poles than other tents, making them heavier to carry in a pack, and stuffy if the weather is warm. However, adequate shelter and sleep can mean the difference between life and death at high altitude, so it's better to be safe than sorry. Choose a sleeping bag and tent rated to withstand the lowest temperatures you expect to face; you can always unzip a tent flap or shed a layer of clothing if you get too warm.
Once you've chosen your sleeping bag and tent, it's time to think about other gear you'll need to pack. Is the air really so thin at high altitude that matches won't light? Find out next.