The Thaumonomicon is a very useful tool throughout Thaumcraft. It lists all the research you have discovered, as well as somewhat detailed information about that research, such as crafting recipes and their uses. It also shows the basic tree of research, and faded images of undiscovered research, giving hints as to what might be needed to obtain them. The Thaumonomicon is created by using a Casting Wand on a bookshelf.
To craft the Thaumonomicon, you must simply use(right-click) your wand on a bookshelf placed in the world. Note that the bookshelf will be consumed.
The Thaumonomicon is a reference book of all things thaumaturgical. It lists all the discoveries you have made so far and gives you a general impression of how many there are still to be made.
Whenever you successfully research something and use the scroll, it will automatically be added to this book. You can then browse through the discoveries and click on them to be shown more detailed information regarding them.