For much of the public, Jewish Orthodoxy may be defined by Tevye from "Fiddler on the Roof" or Barbra Streisand in "Yentl," but Orthodoxy is a far more nuanced, vast, and splintered world than those portraits suggest. Picture Joseph Lieberman next to Tevye, and you have an idea of the spectrum that Orthodoxy covers. Modern Orthodox Jews, with their, well, modern attire and often clean-shaven faces are a world apart from ultra-Orthodox Jews, with their black clothes, black hats, beards for men, and dangling earlocks.

The clothes embody vastly different worldviews. Ultra-Orthodox Jews believe in separating themselves almost entirely from the potentially corrupting influences of modern culture. Their communities tend to be nearly exclusively populated by other ultra-Orthodox Jews, their customs hark back directly to those of their ancestors in Eastern Europe, and those who pursue "secular" professions tend to practice them in ultra-Orthodox communities or companies.

Modern Orthodox Jews, however, model their lives on the relatively recent theological notion of Torah u'Madah, literally, Bible and science. This means dwelling in two worlds simultaneously, the religious world of traditional Jewish observance and the secular world of American culture and professional life. It does not mean that these Orthodox Jews live in a religious world on Saturday, the Sabbath, and a secular world during the week. It means, quite literally, that they exist in both worlds at once, living a life in tension between the two and negotiating compromises between them. It is a life modeled on the moral and religious teachings of Judaism, but one which engages, rather than shies away from, modern society, which modern Orthodox Jews no less than ultra-Orthodox ones see as potentially corrupting.

So what are the teachings and traditions on which that lifestyle and worldview are based? Orthodoxy, as its name implies, believes in strict adherence to Jewish law, believing halakah, the Hebrew term for Jewish law, to be the direct will of God as it was revealed to Moses at Sinai. Halakah is derived from the Torah (the Hebrew Bible), the Talmud (the compilation of rabbinic disputation, discussion, and exegesis compiled around 600 C.E. ), and law books and rabbinic rulings throughout the centuries, up to the present day. The vast canon of Jewish law covers every aspect of personal and communal life, even those many people might consider secular or otherwise outside the purview of religion. Halakah lays out not only how Jews should worship God but how they should conduct their relationships, business affairs, personal conduct, and communal life. Myriad laws, for example, detail the minutiae of avoiding gossip, describing in great detail what types of statements are permitted and what are prohibited. Others instruct business owners on avoiding unfair competitive practices or lay out a process for dealing with the ownership of lost items found in a public area.

Of course, much of Jewish law does deal with the specifically "religious" aspect of life. Orthodox Jews' daily routine consists of many "religious" activities. They pray three times a day, either in a synagogue or other communal setting or by themselves. Afternoon and evening prayers are short, taking maybe five or 10 minutes to complete, while morning prayers are longer, perhaps 45 minutes or an hour. Halakah dictates one-line blessings to be recited before any food or drink is consumed, and somewhat longer prayers of thanksgiving to be said at the end of meals.

Two of the more well-known and important aspects of Orthodox life are the Sabbath and kosher laws. Shabbat, the Sabbath, runs from sundown Friday to sundown Saturday. It is widely known that "work" is forbidden on Shabbat, but as with so much of Jewish law, the truth is more nuanced than that. Jewish law books lay out 39 tasks that are forbidden on Shabbat, from lighting a fire to using a hammer to spending money. From there, the many restrictions of Shabbat are derived, by analogy and comparison. In modern times, rabbis have used, for instance, the prohibition against lighting a fire to outlaw electricity. They have also restricted driving on Shabbat. The intention is to create a day of peace, removed from the worries of everyday life, when Jews can focus on their religious lives, their families, and their communities. Jews typically keep Shabbat by praying in synagogue Friday night and Saturday morning (many attend Saturday afternoon and evening services as well) and eating large, traditional meals with friends and family.

For Lieberman, Shabbat has meant walking to and from the Capitol when important debates or votes take place Friday night or Saturday. When he was first nominated as a Connecticut senator, Lieberman skipped the nomination convention entirely, since it was held on Saturday, deciding instead to appear via pre-recorded video. Jewish law allows for wide latitude when lives are at stake and mandates that most laws be broken to save lives; Lieberman has said this would allow him to take care of vital affairs of state on Shabbat if he were president.