Ahmed Hassan Zewail (born February 26, 1946 in Damanhour, Egypt) is an Egyptian-American scientist, and the winner of the 1999 Nobel Prize in Chemistry for his work on femtochemistry. He received bachelor's degree and MS degree from the University of Alexandria before moving from Egypt to the United States to complete his PhD at the University of Pennsylvania with advisor Dr. Robin Hochstrasser.

After some post doctorate work at UC-Berkeley, he was awarded a faculty appointment at Caltech in 1976, where he has remained since. He became a naturalized citizen of the United States in 1982, and in 1990, he was made the first Linus Pauling Chair in Chemical Physics.
In 1999, Zewail became the third ethnic Egyptian to receive the Nobel Prize, following Egyptian president Anwar Al-Sadat (1978 in Peace) and Naguib Mahfouz (1988 in Literature). Other international awards include the Wolf Prize in Chemistry (1993) awarded to him by the Wolf Foundation, the Tolman Medal (1997), the Robert A. Welch Award (1997), and the Priestley Medal from the American Chemical Society in 2011. In 1999, he received Egypt's highest state honor, the Grand Collar of the Nile.
Zewail was awarded a PHD. Honoris Causa by Lund University in Sweden in May 2003 and is a member of the Royal Swedish Academy of Sciences. Cambridge University awarded him an Honorary Doctorate in Science in 2006. In May 2008, Zewail received a PhD Honoris Causa from Complutense University of Madrid. In February, 2009, Zewail was awarded an honorary PhD in arts and sciences by the University of Jordan. In May 2010, he received a PhD Honoris Causa in Humane Letters from Southwestern University.