Answer:
   
   Orthodox Judaism is not a unified movement with a single governing
   body, but rather many different movements adhering to common
   principles. All of the Orthodox movements are very similar in their
   observance and beliefs, differing only in the details that are
   emphasized. They also differ in their attitudes toward modern culture
   and the state of Israel. They all share one key feature: a dedication
   to Torah, both Written and Oral.
   
    Origins of the Movement
    
   Historically, there was no such thing as Orthodoxy; in fact, you find
   the particular term is used primarily in North America (elsewhere, the
   distinction is primarily between "more observant" and "less
   observant"). The specific term "Orthodox Judaism" is of rather recent
   origin and is used more as a generic term to differentiate the
   movements following traditional practices from the Liberal Jewish
   movements.
   
    Orthodox Theology
    
   Orthodox Judaism views itself as the continuation of the beliefs and
   practices of normative Judaism, as accepted by the Jewish nation at
   Mt. Sinai and codified in successive generations in an ongoing process
   that continues to this day.
   
   Orthodox Judaism believes that both the Written and Oral Torah are of
   divine origin, and represent the word of G-d*. This is similar to the
   view of the Conservative movement, but the Orthodox movement holds
   that such information (except for scribal errors) is the exact word of
   G-d, and does not represent any human creativity or influence. For the
   details of the Orthodox view of the origin of Torah, see [5]Section
   3.4. For the Orthodox, the term "Torah" refers to the "Written Law" as
   interpreted by the "Oral Law", interpreted in turn by the Rishonim
   (Medieval commentators), and eventually codified in the Codices: R.
   Joseph Karo's Shul`han Arukh and/or R. Moshe Isserlis's Mapah (printed
   as parenthetical text in the Shul`han Arukh). As practical questions
   arise, Orthodox Authorities apply the Halachic process (the system of
   legal reasoning and interpretation described in the Oral Torah) using
   the Torah (both Oral and Written) to determine how best to live in
   accordance with G-d's will as directed by the Halacha. In this way,
   Orthodoxy evolves to meet the demands of the times.
   
   An excellent summary of the core beliefs of Orthodox Judaism may be
   found in the [6]Rambam's 13 Principles of Faith. [For those reading
   the posted version of this, they may be found in Section 4.7 of the
   FAQ]
   
   One of the hallmarks of Orthodox Jews is an openness (and
   encouragement) to question what it is that G-d requires of us, and
   then to answer those questions within the system that G-d gave us.
   
   In addition, among the major movements only Orthodoxy has preserved
   the "mystical" foundations of Jewish theology, most obviously in the
   Chasidic movements though no less so in many Yeshivah movements, both
   Ashkenazi and Sephardi.
   
    Sources for More Information
    
   Additional information may be found in the [7]Traditional Reading
   List, found at http://www.scjfaq.org/rl/tra-index.html.
   
   [*: Some Orthodox Jews include the commentaries and responsa
   literature as part of "Torah". Such works are human attempts to divine
   the meaning of the Written and Oral Torah.]