Followers of Judaism are called Jews, and while Judaism is open to converts, the Jewish collective is regarded as an ethno-religious group, for reasons derived from the sacred texts that define them as a nation, rather than followers of a faith. In 2007, the world Jewish population was estimated at 13.2 million people, 41% of whom lived in Israel. - Wikipedia article "Judaism"

The following links provide a sound basis for the study of Judaism.