Over time I have accumulated a fair number of cookbooks, many of them with glossy photos of exciting recipes, usually received as gifts or bought on impulse... and I rarely use them. They're fun to look through, but I just don't really like cooking from a highly specific, out-of-context recipe. As I've been getting more into cooking, I've found that I really enjoy reading (and then cooking from) books that explain different techniques, how ingredients work together, etc - books that "teach" rather than just present a recipe.
I'd like to add some cookbooks to my Christmas list. Which books do you consider essential in every cook's library? Which books have most shaped/influenced the way that you cook? And/or bake, I should add - I'm not much of a baker but I would love to learn more!