This book covers the whole gamut of photographic filters, explaining what they do, why you would use them with samples of their effects.
While the information contained in this book is essential reading for serious film/slide photographers (both colour and black & white), for the DSLR photographer, much of this is of accademic interest only.
Polarizing, neutral density, and UV filters are probably all a DSLR user will need as most other effects can be achieved using image editing software.
If there is one obvious shortcoming in this book, it is a lack of reference to digital. For example, when refering to colour correction/changing/balancing filters, I would have liked some reference to how these are achieved in Photoshop.
Overall however, a great read. Even if you shoot digital (as I do), you will still need some of these filters and it is useful to be aware of other colour issues.