By Leah:

What might be considered the basic 'primer' for photographers, this is not just for those new to a camera. Rather, this book does an excellent job in clearly laying out the triangle of exposure and finding the right 'creative' exposure that you are going for. These are things most photographers understand on some level, but cannot always articulate. And that inability to articulate can prevent you from knowing immediately what settings to change to get the results you are aiming for.

No photographer should be out there shooting without having read this book at least once, if not several times and running through some of the exercises on exposure and depth of field.

Says David Rosenthal about this book:

Bryan Peterson's "Understanding Exposure" is an outstanding book. He explains exposure in incredibly simple, effective terms and illustrates his discussion with his great photos.

You can find it on Amazon.com: Understanding Exposure: How to Shoot Great Photographs with a Film or Digital Camera