Not a book, but for a technical overview of exposure I recommend the wikipedia entry on [Exposure value](http://en.wikipedia.org/wiki/Exposure_value).
<br>Briefly, you have some level of light in the scene, called LV (light value or luminance value), and a combination of camera settings - shutter speed, aperture and ISO - called EV (exposure value).
They are measured on the same scale, and when LV in the scene equals EV on the camera we have a correct exposure. 
<br>_This is "correct exposure" in the rather narrow technical sense of making a [gray card](http://en.wikipedia.org/wiki/Gray_card) show up as 18% gray in the image. This is how camera light meters work: They assume that you want everything in the scene to average out to 18% gray, and will give a night photo the same average brightness as a day photo if you let them._

You will probably want to know about [dynamic range](http://en.wikipedia.org/wiki/Dynamic_range) as well, the ratio between the brightest and darkest luminance a sensor can capture in a single exposure. Many other fields measure dynamic range in dB (log 10 scale), while in photography we most commonly use stops (1 stop = 1 EV, log 2 scale). <br>
Many scenes will have a higher dynamic range than the sensor can capture; then you'll need to decide which parts you are willing to sacrifice. <br>
_Alternatively, look into more advanced topics like HDR or [exposure fusion](http://photo.stackexchange.com/questions/tagged/exposure-fusion), which combine several pictures of the same scene, taken with different EV settings, into a single image._

The [Zone System](http://en.wikipedia.org/wiki/Zone_System) is based on EV and dynamic range: You pick a single spot in your scene and decide how bright or dark you want it to appear in the photo, and adjust the EV from the light meter reading accordingly. 
<br>The question ["What is Ansel Adams' Zone System"](http://photo.stackexchange.com/questions/6769/what-is-ansel-adams-zone-system) has a nice overview with example pictures.

As far as the technical aspects of exposure go, that's pretty much it. 

There are also various effects of choosing different shutter speed/aperture/ISO combinations for the same exposure, but those are different topics. (Primary keywords: Motion blur, depth of field and high-ISO noise.)