A lot depends on what you already know ... but if you are starting from square one:
Joy of Cooking (either the 1975 or 1995 edition) by Irma S. Rombauer and Marion Rombauer Becker should be in every cooks collection. Not just for the recipes - but for the "about" information on the things we cook.
Cookwise: The Secrets of Cooking Revealed by Shirley Corriher - a noted food scientist explains how things work and gives recipes that use those principles. A good introduction to food chemistry and applying those lessons to cooking.
On Food and Cooking: The Science and Lore of the Kitchen (Revised Edition) by Harold McGee starts to get you into the real chemistry of food.
The Cusious Cook by Harold McGee takes you into the kitchen as a lab and answers some interesting questions using experiments to discover the answers. Things like: why does a cook end up with more grease on the inside of their glasses than on the outside; does searing meat really lock in the juices; is rinsing mushrooms off really bad? If you saw Alton Brown's MythSmashers episode you get where this book is headed - and where AB got most of his inspiration for that show. [This book can be hard to find especially at anything close to the original cover price]
What Einstein Told His Cook: Kitchen Science Explained and What Einstein Told His Cook 2: The Sequel - Further Adventures in Kitchen Science by Robert L. Wolke. Wolke is a Chemist - and a professer - so takes a little different approach than McGee ... a little less technical, a little easier to read and understand by the average home cook without a science background. But, it's not a comic-book version of classic literature, either.
Once you are armed with those books .... then you might want to consider some of the CRC Handbooks - Chemistry and Physics, Biochemistry and Molecular Biology, Mathematical Curves and Surfaces (you can use this in calculating some of what McGee is talking about in The Curious Cook regarding heat transfer through various shaped pieces of meat). It just depends on how far you want to go with the "theoretical science" side of cooking.
Now that you are armed with more science than you know what to do with ... but still being the curious cook and wondering about what would happen if you made a recipe one way vs another ....
The Best ... series of cookbooks from the folks at Cook's Illustrated Magazine/America's Test Kitchen. They take you through the process of taking a recipe, trying different approaches, explains what did and didn't work (and why), and come up with what they consider to be the best result. Think of it as a series of experiments of practical applications of theoretical knowledge in search of solving for the unknown process and ingredients to achieve a known result.
Now - I've know cooks who never knew what chemicals comprised the flavor of an herb ... but knew what it tasted like and knew the flavor of similar herbs - so they knew what they could substitute. They didn't know a thing about how proteins denature - but always made perfect meals. But, I'll admit that knowing the science behind the scenes can be fun, too.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain