Orthodox Judaism is a group of different movements adhering to common orthodox principles (strict interpretation and application of the laws and ethics of the Talmudic texts). They all share one key feature: a dedication to Torah. However, their attitudes toward modern culture and the state of Israel could differ. Orthodox Judaism is the most traditional branch of Judaism. There are about half a million Orthodox Jews in the United States.
Orthodoxy evolves to meet the demands of the times. An excellent summary of the core beliefs of Orthodox Judaism may be found in the Rambam's 13 Principles of Faith... One of the hallmarks of Orthodox Jews is an openness (and encouragement) to question what it is that Gd requires of us, and then to answer those questions within the system that Gd gave us. 
The Orthodox Union and the Rabbinical Council of America, are organizations that represent Modern Orthodox Judaism.
Orthodox Jews are more likely to vote Republican than members of other branches of Judaism.
"The likelihood is there will be a very quick jump in the number of orthodox as the baby boomers age and die," said David A. Harris of the American Jewish Committee, a nonpartisan organization that conducts an annual survey of Jews. "They will be increasingly replaced by Orthodox children who are more" in line with Republicans.
Researchers commissioned by the American Jewish Committee found that the group most receptive to the GOP message is Orthodox Jews. They are much more likely to base their political decisions on a candidate's view on Israel than other Jews, researchers have found.
Bush has made small gains among Jews since his first election, but short of what some GOP strategists had envisioned. A staunch supporter of Israel who won the backing of a few prominent Democratic Jews such as former New York City mayor Ed Koch, Bush captured between 22 and 26 percent of the Jewish vote in 2004, based on various exit polling surveys. In 2000, he won 19 percent.
Orthodox Jews are the fastest growing segment of the Jewish population.
Orthodox Judaism is the only branch of Judaism in USA which has a net gain for each generation, for Conservative Jews there was on average 1.74 children per mother, for Reform there was on average 1.36 children per mother, for Secular Jews there was on average 1.29 children per mother, for Orthodox Jews there was on average 3 to 7 children per mother. Amongst Orthodox the lowest rate of intermarriage was found at 6% while amongst Conservative Jews the intermarriage rate was 32%, amongst Reform Jews it was 46%, and amongst Secular Jews it was 49%. Amongst Orthodox Jews the intermarriage has been decreasing with each generation while amongst non-Orthodox Jews the intermarriage rate is increasing. Of children born through intermarriage only 28% of them are raised as Jewish. And of children of intermarriage who identify as Jewish only 10 to 15% of them end up marrying Jews. The combination of Jewish commitment and having experienced a complete K-12 Orthodox Jewish Day School education results in an intermarriage rate of not greater than 3%. Explaining why Orthodox have such a low rate of intermarriage. All the research indicates that it is essentially the Orthodox who are committed to such a complete Day School education.
Within three generations there will be almost no trace of young American Jews who are currently not being raised in Orthodox homes with a complete Jewish Day School education. 
While only 7.8% of Jews aged over 70 are Orthodox, 9.7% of those aged 30-69 are Orthodox and between the ages of 18-29, the Orthodox percentage is 19.5%. Furthermore, approximately 27% of all Jewish children under the age of 18 are being raised in Orthodox families. It is also interesting to note that according to the NJPS 2000, although only 46% of US Jews belong to synagogues, that minority divides up 39% Reform, 33% Conservative, 21% Orthodox and 7% Other. If synagogue affiliation continues to be an important “bell weather” of the denominational forecast for the years ahead, Orthodoxy is capturing a growing market. More specifically, between the ages of 18-34, 34% of Jewish adults who are synagogue members have chosen to belong to an Orthodox synagogue 
This confirms another study which showed that Jews, who regularly attend synagogue are having children at a higher rate than other Jews.