Alexander Alexandrovich Kirillov Jr. () is a Russian-born American mathematician, working in the area of representation theory and Lie groups. He is a son of Russian mathematician Alexandre Kirillov.
Kirillov received his master's degree from Moscow State University in 1989 and Ph.D from Yale University in 1995. He is currently a professor at State University of New York at Stony Brook.
Kirillov is a teacher of the project School Nova, trying to establish traditions of the Russian Mathematical Schools on American soil.
He is also a member of the international volunteer organization Rubikus.HelpUA that helps Ukrainian refugees stranded in Russia after the Russian invasion of Ukraine to evacuate to EU.