Satmar (Yiddish: סאַטמאַר; Hebrew: סאטמר) is a group in Hasidic Judaism founded in 1905 by Grand Rebbe Joel Teitelbaum (1887–1979), in the city of Szatmárnémeti (also called Szatmár in the 1890s), Hungary (now Satu Mare in Romania). The group is a branch of the Sighet Hasidic dynasty. Following World War II, it was re-established in New York and has since grown to become one of the largest Hasidic dynasties in the world, comprising around 26,000 households making up a population of nearly 300,000.

Satmar is characterized by extreme conservatism, complete rejection of modern culture, and strong religious anti-Zionism. The community sponsors a comprehensive education and media network in Yiddish, which is also the primary language used by its members. Satmar also sponsors and leads the Central Rabbinical Congress, which serves as an umbrella organization for other highly conservative, anti-Zionist, and mostly Hungarian-descended ultra-Orthodox communities.

Following the death of Joel Teitelbaum in 1979, he was succeeded by his nephew, Moshe Teitelbaum. Since Moshe's death in 2006, the dynasty has been divided between his two sons, Aaron and Zalman Leib, each leading separate communities and institutions.

According to the research of Marcin Wodziński, around 2016, the group consisted of 26,078 households, making up 20.2% of the world Hasidic population and being the largest Hasidic group in the world.

Chananya Yom Tov Lipa Teitelbaum was the Grand Rebbe of the Sighet Hasidic dynasty. He died in 1904, and was succeeded by his oldest son, Chaim Tzvi Teitelbaum.

A few Sighet Hasidim preferred his second son, Joel, as their leader. Joel Teitelbaum left the town of Máramarossziget, and, on 8 September 1905, he settled in Szatmárnémeti (in Yiddish: Satmar). His Sighet supporters followed him, and he began to attract a following. Hungarian journalist Dezső Schön, who researched the Teitelbaum rabbis in the 1930s, wrote that Teitelbaum started referring to himself as the "Rebbe of Satmar" at that time.

Teitelbaum's power base grew with the years. In 1911, he received his first rabbinical post as chief rabbi of Ilosva. In 1921, the northeastern regions of Hungary were ceded to Czechoslovakia and Romania, under the terms of the Treaty of Trianon. This area was densely populated with a segment of Orthodox Jewry known as Unterlander Jews. Many Sziget Hasidim, unable to regularly visit Chaim Tzvi's court, turned to Joel Teitelbaum instead.

In 1925, Teitelbaum was appointed chief rabbi of Carei (Nagykároly). On 21 January 1926, Chaim Tzvi died unexpectedly, leaving his twelve-year-old son Yekusiel Yehuda to succeed him. Their mother emphasized Joel as successor, her grandson being too young for the position, and Joel returned to Sziget. However, Chaim Tzvi's followers would only accept Joel as a trustee-leader until Yekusiel became old enough. Although Teitelbaum was highly regarded, he was not well-liked there. Under these conditions, Teitelbaum would have become the dynasty's head in all but name, which was nevertheless unacceptable for him and his mother, and they left Sziget again. In 1928, Teitelbaum was elected as chief rabbi of Szatmárnémeti itself. The appointment resulted in bitter strife within the Jewish community, and he only accepted the post in 1934.