Origins of Judaism
For centuries, the traditional understanding has been that Judaism came before Christianity and that Christianity separated from Judaism some time after the destruction of the Second Temple in 70 CE. Starting in the latter half of the 20th century, some scholars have begun to argue that the historical picture is quite a bit more complicated than that. In the 1st century, many Jewish sects existed in competition with each other, see Second Temple Judaism. The sects which eventually became Rabbinic Judaism and Early Christianity were but two of these. Some scholars have begun to propose a model which envisions a twin birth of Christianity and Judaism rather than a separation of the former from the latter. For example, Robert Goldenberg (2002) asserts that it is increasingly accepted among scholars that "at the end of the 1st century CE there were not yet two separate religions called "Judaism" and "Christianity"".
Daniel Boyarin (2002) proposes a revised understanding of the interactions between nascent Christianity and nascent Rabbinical Judaism in Late Antiquity which views the two religions as intensely and complexly intertwined throughout this period.
Orthodox Judaism
In the State of Israel, where the total Jewish population is about 6.5 million, 22% of all Jewish respondents to a 2016 PEW survey declared themselves as observant Orthodox (9% "Haredim", or "Ultra-Orthodox", 13% "Datiim", "religious"). 29% described themselves as "traditional", a label largely implying little observance, but identification with Orthodoxy. The second largest Orthodox concentration is in the United States, where a 2013 PEW survey found that 10% of respondents identify as such, in a total Jewish population of at least 5.5 million. 3% were Modern Orthodox, 6% were Ultra-Orthodox, and 1% were "other" (Sephardic, liberal Orthodox, etc.) In Britain, of 79,597 households with at least one Jewish member that held synagogue membership in 2016, 66% affiliated with Orthodox synagogues: 53% in "centrist Orthodox", where congregants are often lax in observance, and 13% in "strictly Orthodox" (further 3% were Sephardi, which technically eschews the title "Orthodox").