This introduction presents an overview of the key concepts discussed in this book. The book describes, analyzes and explains the reasons for the religionization of Israeli society, a process known in Hebrew as hadata and widely recognized and discussed in academia and in the public sphere. Our understanding of religion, following Talal Asad, William Cavanaugh, and many others, is a non-essentialist one: the term "religion" for us does not connote a trans-historical, trans-cultural, universal phenomenon. The close connection between the emergence of religion as a distinct category and the development of nationalism and the nation-state had a dual effect on the Jews of Europe. The emergence of Zionism as a secular political movement actively seeking to "return" the Holy Land to Jewish sovereignty constituted a formidable theological dilemma for Orthodox Jews, a dilemma which has been aggravated by the Holocaust and by every Zionist success.