In the index to this book I have tried to cater both to those who have already read the book in detail, and to those who have not. My approach has generally been to include any term that might realistically come to mind when thinking of a given topic—or remembering what the book says about that topic. And this means that even if the book mentions a term only in passing, I have tended to include it if for one reason or another I think it is likely to be memorable to people with certain experience or interests. Note that looking up Mathematica functions used in connection with some issue is often a good way to identify related issues. In the actual building of the index in this book, sorting, processing and checking were done using a variety of automated Mathematica procedures, operating on a symbolic representation of the full text and index of the book. Often it is possible by reading an index to identify the important issues in a book. And to some extent that is possible here, though often the presence of more subentries just reflects material being more spread out, not more important.