This book contains the same information found in the book No Pattern Knits by the same authors. This book appears to be an earlier version, and I think a more complete one. I was able to check No Pattern Knits out from the library. When I saw this book I had to wonder if it was about the same as the other. Well, it is, and it isn't. The information is the same, but there is a lot more of it in this book. I felt that this book gives more inspriration than the other title. It contains no actual patterns. All the pictures are line drawings except for a few color plates. They stated that they did this so you would not be distracted by the colors, but concentrate on the shapes. The other title is more recent and is full of color pictures. It also contain a few patterns to get you going. But, I don't think it is contains as much written info. and wasn't as inspiring to me. So, either is fine, but I don't really think you need both. Depending on what your preference is, either is good to learn modular knitting from.
UPDATE: I checked the No Pattern Knits out again to make sure my memory was correct. Now that I've seen it again, I really think both books would be good to have. While the majority of the information is the same, they both also contain info that the other book doesn't have. And the pictures in the more recent book are outstanding. The patterns are cute too. I still think Woolly Thoughts has more technical info. Both would be great additions to your knitting library.