Introduction to Orthodox Judaism
Orthodox Judaism is the type of Judaism which has been practiced for thousands of years. It is the oldest of the three monotheistic religions.
Fundamental beliefs 
The fundamental beliefs of Orthodox Judaism are listed in the thirteen principles of faith, compiled by the Rambam. According to some authorities, when a Jew does not acknowledge these principles, it may constitute kefirah (heresy). Following is an English translation of the slightly adapted version which is included in most siddurim (prayer books) at the conclusion of shacharis (the morning service).
- I believe with perfect faith that G-d is the Creator and Ruler of all things. He alone has made, does make, and will make all things.
- I believe with perfect faith that G-d is One. There is no unity that is in any way like His. He alone is our G-d He was, He is, and He will be.
- I believe with perfect faith that G-d does not have a body. physical concepts do not apply to Him. There is nothing whatsoever that resembles Him at all.
- I believe with perfect faith that G-d is first and last.
- I believe with perfect faith that it is only proper to pray to G-d. One may not pray to anyone or anything else.
- I believe with perfect faith that all the words of the prophets are true.
- I believe with perfect faith that the prophecy of Moses is absolutely true. He was the chief of all prophets, both before and after Him.
- I believe with perfect faith that the entire Torah that we now have is that which was given to Moses.
- I believe with perfect faith that this Torah will not be changed, and that there will never be another given by G-d.
- I believe with perfect faith that G-d knows all of man's deeds and thoughts. It is thus written (Psalm 33:15), "He has molded every heart together, He understands what each one does."
- I believe with perfect faith that G-d rewards those who keep His commandments, and punishes those who transgress Him.
- I believe with perfect faith in the coming of the Messiah. How long it takes, I will await His coming every day.
- I believe with perfect faith that the dead will be brought back to life when G-d wills it to happen.
Orthodox Judaism is divided into numerous streams. The following is an attempt to clarify this division. Movements within the Orthodox Jewish world are frequently referred to as 'left-wing' or 'right-wing'.
- Modern Orthodox Judaism (also known as Religious Zionist Judaism, National Religious Judaism)
- Left-wing Modern Orthodox Judaism
- Centrist Modern Orthodox Judaism
- Right-wing Modern Orthodox Judaism
- Chareidi Judaism (also known as ultra-Orthodox Judaism, Chareidi Judaism)
- Lithuanian Judaism, commonly referred to as Yeshivish or Litvish
- Chassidic (Hasidic) Judaism, commonly referred to as Chassidish
- Sepharadi Judaism, many Sepharadi (and Temani [Yeminite]) Jews are also affiliated to the Haredi Branch or ultra-Orthodox Judaism.
There are many different subcategories, especially regarding Chassidic Judaism, which consists of numerous chassidic groups, led by Rebbes.
Some important differences between Modern Orthodox Judaism (from here on referred to as MOJ) and Chareidi Judaism are the following:
- MOJ believes in combining secular education and Jewish education, while Chareidi Judaism fundamentally rejects secular education, though depending on the specific group of Chareidim, it is usually acknowledged that a certain amount of secular education is necessary in order to be able to earn an income.
- MOJ believes that Jews need not dress in a significantly distinctive way (provided that one's dress is somewhat modest), while Chareidi Judaism places great emphasis on a traditional style of dress.
- MOJ generally equals religious Zionism, while a few Chareidi Judaism oppose especially when Zionism is equated with a ssecular homeland for the Jews.
- Chareidi Judaism places a much stronger emphasis on tradition than MOJ does. For example, all Ashkenazi Chareidim use the Ashkenazi pronunciation of Hebrew, while nearly all Ashkenazi Modern Orthodox Jews have switched to the Sephardic pronunciation (which is used for Modern Hebrew of the State of Israel).
- Chareidi Judaism maintains a much stronger separation of the genders. This separation is different in Chassidic Judaism than in Lithuanian Chareidi Judaism (for example, while in Lithuanian Chareidi girls schools there are male teachers, Chassidic girls schools consider this to be completely forbidden).
- Chareidi Judaism places great emphasis on Chareidi Jews living together in distinct neighborhoods, away from other cultures, which are perceived as threatening Chareidi children.
Despite these differences, Modern Orthodox and Chareidi Jews share the same theological principles of faith (see above) and have no problems joining each other's prayer services (though from the Chareidi side this requires that some requirements, such as the separation between the men's section and women's section, are met according to Halacha as determined by Chareidi poskim, which might not always be the case especially in left-wing Modern Orthodox synagogues).