Handbook of Jewish Thought Volume I By Rabbi Arieh Kaplan

There are a number of great ideas that literally form the backbone of Judaism. Without the knowledge of these ideas, it is virtually impossible to know how Judaism came to be as it is today, or how it functions. Unfortunately, however, the more important the idea, the less the average person knows about it. The Handbook therefore comes to fill this void 
This is Volume I by Rabbi Aryeh Kaplan.