The Kuzari is the classic Medieval book by Rabbi Yehuda HaLevi that provides a rational defense of Judaism against the polemics of Christianity, Islam and secular Philosophy.

The book itself is important reading for any Jewish educator.

The basic Kuzari argument is eloquently articulated using modern examples in these three links:

1. Modern Kuzari – Lecture Format
2. (Audio mp3 version of #1)
3. Modern Kuzari – Graphical Format