This is an incredibly short book, one I read in about 2 hours, but one that leaves you reeling for the rest of your life. Kaplan simply serves as translator and editor to the words of that great Jewish sage, Maimonides, who, in his Commentary to the Mishna, and his Mishne Torah, among others, compiled and commented on what he understood to be the principles of Jewish faith. These 13 principles define the core beliefs of Judaism with a clarity and conciseness that bespeaks of Maimonides' high intelligence and spirituality more than 800 years after they were first written. In this book, we are given each of the principles, with Maimonides' words of explanation taken from his various works, presenting in simple language the practical applications of each principle, a gift to every reader, regardless of how much you have studied. The maxim says good things come in small packages, and this book proves it. Every Jew should own this book, and everyone interested in Judaism should absolutely read it (heck, I think Christians would benefit from reading it as well--as an offspring of Judaism, Christianity would do well to know the foundation of its parent religion, both to learn what makes us different, but also to understand how we view G-d, and how we can come to a mutual understanding, respecting each other's beliefs). Like I said, a small book that will affect you for the rest of your life.
Kaplan provides a lucid little discussion of Rambam’s 13 principles, but adds more translation and collection than analysis. Artscroll also reprinted this book in volume 1 of The Aryeh Kaplan Anthology.