Mousa Mohammed Abu Marzook (Arabic: موسى محمد أبو مرزوق‎; born 9 January 1951) is a Palestinian politician and senior member of Hamas who served as the first chairman of the Hamas Political Bureau from 1992 until 1996 and deputy chairman of the Hamas Political Bureau from January 1997 until April 2013, where he was succeeded by Ismail Haniyeh.

Marzook's parents were from Yibna, (now Yavne, Israel). During the 1948 Arab–Israeli War they were expelled to Rafah Camp in the Gaza Strip. Marzook was born there on 9 January 1951, the second of nine children. During the Six Day War, Marzook's brother Mahmud Abu Marzook joined a fighting force that became a military unit of the Palestine Liberation Organization. As a teenager in Rafah, Marzook was introduced to Sheikh Ahmed Yassin, a member of the secret leadership of the Egyptian Muslim Brotherhood.

Marzook completed high school in Gaza, studied engineering in Cairo from 1970 to 1976, and worked as an engineer in Abu Dhabi. By then, he was active in the Muslim Brotherhood. Marzook was an inaugural member of the board of the Islamic University of Gaza, founded by Islamists in 1978. Marzook travelled extensively throughout the Middle East during his years in Abu Dhabi, cultivating political and financial connections in support of his goal to establish an independent Islamist state in Palestine.

In 1982, he traveled to the United States on a student visa. Marzook earned a master's degree in construction management from Colorado State University, then a Doctorate degree in Industrial Engineering from Louisiana Tech University.

In 1991, he moved to Springfield, Virginia. Marzook lived in the U.S. for at least 14 years, obtaining a Green Card in 1990. He is married with six children.

From the founding of Hamas at the end of 1987, Marzook became its leading political voice. Abu Marzook was elected as the first head of the Hamas Political Bureau in 1992, overseeing its operations from Northern Virginia under the United Association for Studies and Research. According to U.S. officials, up to 15 percent of Hamas's $70 million annual budget came from America. Journalist Shlomi Eldar credits Abu Marzook's fundraising prowess, and his connections to donors in Europe and the US with saving the organization and developing its infrastructure in Gaza, including social service programs. Israel claims that some funds were used for attacks against Israel, a charge that Abu Marzouk denies. Since 1997 has been deputy chairman of the Hamas Political Bureau. Marzook lived in Jordan from 1998 to 2001. He then moved to Damascus, Syria in 2001.

From 1991 until 1995, Marzook held secret talks with U.S. government officials as the leader of Hamas in the United States. During meetings, Marzook reportedly explained Hamas's conditions for talks with Israel and pledged not to conduct operations against the United States. According to U.S. officials, Marzook traveled to Tehran in October 1992 in his role as Hamas's de facto foreign minister. On August 1, 1993, Marzook reestablished the Hamas Political Bureau in Amman, returning to the United States three or four times per year to renew his green card and meet with U.S. officials. On July 1, 1995, Jordanian Prime Minister called Marzook and expelled him from Jordan, claiming pressure from Israel. Israel held Marzook responsible for overseeing segments of Hamas that killed 47 Israelis between 1990 and 1994, claimed by Hamas' military wing.

Marzook founded the Islamic Association of Palestine.