If you are a serious fan of TMI/TID, you should read this. You should also know that you do not HAVE to read this. There is no interesting hidden information that you need in order to enjoy the series. This book is comprised of essays, written by authors other than Cassandra Clare, which focus on topics relevant to and contained within Clare's books (i.e the history of tattoos and how it relates to the idea of Shadowhunter runes, or how Judaism and Vampirism are connected). Some of these essays are brilliant (Sarah Rees Brennan's essay on deviance was particularly hilarious, and that aforementioned essay on Judaism and vampires was fascinating, among others) and some are a bit boring (possibly because I didn't click with the specific writing style or topic), or downright disgusting and creepy (there is an essay devoted to discussing Jace and Clary's pseudo-incestuous love and the incest taboo in general. It was disturbing, to say the least.) If you are not a reader who enjoys essays that relate to and analyze books, then you might want to reconsider reading this, no matter how much you love TMI/TID. If, however, you are a reader who loves Clare's books, enjoys literary analysis, and wants to get some fresh and interesting and sometimes disturbing viewpoints on a variety of subjects from some excellent authors, then you should go and get this immediately.