Rabbi Moses Maimonides, also known as Rambam, was the preeminent medieval Jewish philosopher and one of the greatest Torah scholars of the Middle Ages. He was born in Cordoba, Spain on Passover Eve, 1135, and died in Egypt on 20th Tevet, December 12, 1204. He was a rabbi, physician and philosopher in Morocco and Egypt. Although his writings on Jewish law and ethics met with respectful opposition during his life, he was posthumously acknowledged to be one of the foremost rabbinical arbiters and philosophers in Jewish history, his copious work a cornerstone of Jewish scholarship. His fourteen-volume Mishneh Torah still carries canonical authority as a codification of Talmudic law. In the Yeshiva world he is known as "Hanesher Hagadol" (the great eagle) in recognition of his outstanding status as a bona fide exponent of the Oral Torah, particularly on account of the manner in which his Mishneh Torah is elucidated by Chaim Soloveitchik.

His full Hebrew name is Rabbi Moshe ben Maimon, whose acronym forms "Rambam". In Latin, the Hebrew "ben" (son of) becomes the Greek-style suffix "-ides" to form "Moses Maimonides". Maimonides was born during what some scholars consider to be the end of the golden age of Jewish culture in Spain, after the first centuries of the Moorish rule. At an early age, he developed an interest in the exact sciences and philosophy. In addition to reading the works of Muslim scholars, he also read those of the Greek philosophers made accessible through Arabic translations. Maimonides was not known as a supporter of mysticism. He voiced opposition to poetry, the best of which he declared as false, since it was founded on pure invention, and this too in a land which had produced such noble expressions of the Hebrew and Arabic muse. This Sage, who was revered for his saintly personality as well as for his writings, led an unquiet life, and wrote many of his works while travelling or in temporary accommodation. Maimonides studied Torah under his father Maimon, who had in turn studied under Rabbi Joseph ibn Migash, a student of Isaac Alfasi.

The Almohades conquered Cordoba in 1148, and threatened the Jewish community with the choice of conversion to Islam, death, or exile. Maimonides's family, along with most other Jews, chose exile. For the next ten years they moved about in southern Spain, avoiding the conquering Almohades, but eventually settled in Fes in Morocco, where he studied at the University of Al-Karaouine. During this time, he composed his acclaimed commentary on the Mishnah in the years 1166–1168. Following this sojourn in Morocco, he and his family briefly lived in the Holy Land, before settling in Fostat, Egypt around 1168. While in Cairo he studied in Yeshiva attached to a small synagogue that bears his name. In the Holy Land, he prayed at the Temple Mount. He wrote that this day of visiting the Temple Mount was a day of holiness for himself and his descendants. Maimonides shortly thereafter became instrumental in helping rescue Jews taken captive during King Amalric's siege of the Egyptian town of Bilbays. He sent five letters to the Jewish communities of Lower Egypt asking them to pool money together to pay the ransom. The money was collected and then given to two judges sent to Palestine to negotiate with the Crusaders. The captives were eventually released.

Following this triumph, the Maimonides family gave their savings to the youngest son David, a merchant, in the hopes of expanding their wealth. Maimonides directed him to procure goods only at the Sudanese port of Aydhab, but, after a long arduous trip through the desert, David did not like the goods offered in the port city. So he boarded a ship to India against his brother's wishes since great wealth was to be found in the East. Sadly, David drowned at sea sometime between 1169–1170 before he could make it to India. The death of his brother caused Maimonides to become sick with grief. In a letter discovered in the Cairo Geniza, he later explained: The greatest misfortune that has befallen me during my entire life, worse than anything else, was the demise of the saint, may his memory be blessed, who drowned in the Indian sea, carrying much money belonging to me, him, and to others, and left with me a little daughter and a widow. On the day I received that terrible news I fell ill and remained in bed for about a year, suffering from a sore boil, fever, and depression, and was almost given up. About eight years have passed, but I am still mourning and unable to accept consolation. And how should I console myself? He grew up on my knees, he was my brother, [and] he was my student.

Following his recovery, he was appointed the Nagid of the Egyptian Jewish community around 1171. Arabist S.D. Goitein believes the leadership he displayed during the ransoming of the Crusader captives led to this appointment. But since the Maimonides family had their savings tied up in David's business venture, when he drowned, all of that money was lost. This forced Maimonides to take up his famous vocation as a physician. Maimonides was trained as a physician in Cordoba and in Fes. He gained widespread recognition and became a court physician to the Grand Vezier Alfadil, then to Sultan Saladin, after whose death he remained a physician to the royal family. In his writings he described many conditions including asthma, diabetes, hepatitis, and pneumonia, and emphasized moderation and a healthy life style. His treatises became influential for generations of physicians. He was knowledgeable about Greek and Persian medicine, and followed the principles of humorism in the tradition of Galen, however, he did not blindly accept authority but used his own observation and experience. However, in his medical writings he sought not to explore new ideas but to interpret works of authorities so that they could become acceptable. Maimonides displayed in his interactions with patients attributes that today would be called intercultural awareness and respect for the patient's autonomy. In a famous letter, he describes his daily routine: After visiting the Sultan’s palace, he would arrive home exhausted and hungry, where "I would find the antechambers filled with gentiles and Jews ... I would go to heal them, and write prescriptions for their illnesses ... until the evening ... and I would be extremely weak."

Maimonides died on the 20th of Tevet 4965 (December 12, 1204) in Fustat, Egypt where it is believed that he was shortly buried before being reinterred in Tiberias, a town on the western shore of the Sea of Galilee, Lower Galilee, Israel. However the location of Maimonides grave is not without controversy and in the Jewish Cairene community there is tradition that maintains that his grave has remained in Egypt. Maimonides and his wife, the daughter of one Mishael ben Yeshayahu Halevi, had one child, Avraham, who was recognized as a great scholar, and who succeeded him as Nagid and as court physician at the age of eighteen. He greatly honored the memory of his father, and throughout his career defended his father's writings against all critics. The office of Nagid was held by the Maimonides family for four successive generations until the end of the 14th century. He is widely respected in Spain and a statue of him was erected in Cordoba in the only synagogue in that city which escaped destruction. Although no longer functioning as a Jewish house of worship, it is open to the public.

Maimonides was one of the most influential figures in medieval Jewish philosophy. A popular medieval saying that also served as his epitaph states, From Moshe (of the Torah) to Moshe (Maimonides) there was none like Moshe. Radical Jewish scholars in the centuries that followed can be characterised as "Maimonideans" or "anti-Maimonideans." Moderate scholars were eclectics who largely accepted Maimonides's Aristotelian world view, but rejected those elements of it which they considered to contradict the religious tradition. Such eclecticism reached its height in the 14th–15th centuries. The most rigorous medieval critique of Maimonides is Hasdai Crescas' Or Adonai. Crescas bucked the eclectic trend, by demolishing the certainty of the Aristotelian world view, not only in religious matters, but even in the most basic areas of medieval science (such as physics and geometry). Crescas's critique provoked a number of 15th century scholars to write defenses of Maimonides.

In his commentary on the Mishneh (tractate Sanhedrin, chapter 10), Maimonides formulates his 13 principles of faith. They summarized what he viewed as the required beliefs of Judaism with regards to:

1. The existence of G-d
2. G-d's unity
3. G-d's spirituality and incorporeality
4. G-d's eternity
5. G-d alone should be the object of worship
6. Revelation through G-d's prophets
7. The preeminence of Moses among the prophets
8. G-d's law given on Mount Sinai
9. The immutability of the Torah as G-d's Law
10. G-d's foreknowledge of human actions
11. Reward of good and retribution of evil
12. The coming of the Jewish Messiah
13. The resurrection of the dead

With Mishneh Torah, Maimonides composed a code of Jewish law with the widest possible scope and depth. The work gathers all the binding laws from the Talmud, and incorporates the positions of the Geonim (post-Talmudic early Medieval scholars, mainly from Mesopotamia). While Mishneh Torah is now considered the fore runner of the Arbaah Turim and the Shulchan Aruch (two later codes), it met initially with much opposition. There were two main reasons for this opposition. Firstly, Maimonides had refrained from adding references to his work for the sake of brevity. Secondly, in the introduction, he gave the impression of wanting to "cut out" study of the Talmud, to arrive at a conclusion in Jewish law, although Maimonides himself later wrote that this was not his intent. His most forceful opponents were the rabbis of Provence (Southern France), and a running critique by Rabbi Abraham ben David (Raavad III) is printed in virtually all editions of Mishneh Torah. However, it was recognized as a monumental contribution to the systemized writing of Halakha. Throughout the centuries, it has been widely studied and its halakhic decisions have weighed heavily in later rulings.

In response to those who would attempt to force followers of Maimonides and his Mishneh Torah to abide by the rulings of his own Shulchan Aruch or other later works, Rabbi Yosef Karo wrote: "Who would dare force communities who follow the Rambam to follow any other decisor, early or late? ... The Rambam is the greatest of the decisors, and all the communities of the Land of Israel and the Arabistan and the Maghreb practice according to his word, and accepted him as their rabbi." He argued that executing a defendant on anything less than absolute certainty would lead to a slippery slope of decreasing burdens of proof, until we would be convicting merely according to the judge's caprice. Scholars specializing in the study of the history and subculture of Judaism in premodern China (Sino-Judaica) have noted this work has surprising similarities with the liturgy of the Kaifeng Jews, descendants of Persian Merchants who settled in the Middle Kingdom during the early Song Dynasty.

One of the most widely referred to sections of the Mishneh Torah is the section dealing with Tzedakah. In Hilkhot Matanot Aniyim (Laws about Giving to Poor People), Chapter 10:7-14, Maimonides lists his famous Eight Levels of Giving:

1. Giving an interest-free loan to a person in need, giving a grant to a person in need.
2. Giving tzedakah anonymously to an unknown recipient via a person (or public fund) which is trustworthy, wise, and can perform acts of tzedakah with your money in a most impeccable fashion.
3. Giving tzedakah anonymously to a known recipient.
4. Giving tzedakah publicly to an unknown recipient.
5. Giving tzedakah before being asked.
6. Giving adequately after being asked.
7. Giving willingly, but inadequately.
8. Giving "in sadness" - it is thought that Maimonides was referring to giving because of the sad feelings one might have in seeing people in need (as opposed to giving because it is a religious obligation, giving out of pity).