Ibn Rushd or Averroes is one of the most important philosophers in the Islamic tradition, and also one of the most important of all commentators on Aristotle. And Charles Butterworth is one of the premiere translators of Averroes.
This particular text is a very important defense of philosophy against those (in Averroes's specific case, Muslims) who argued that philosophical reasoning is a violation of religious law. Such issues are still alive, more or less (for example, in the struggle between science and religion), so this book has more than merely antiquarian interest.
The translation is very clear, and, for those who read Arabic, it's helpful to have the original text on the facing page. Given the quality of the work, too, the book is surprisingly inexpensive.