Rational lattices occur throughout mathematics, as in quadratic forms, sphere packing, Lie theory, and integral representations of finite groups. Studies of high-dimensional lattices typically involve number theory, linear algebra, codes, combinatorics, and groups. This book presents a basic introduction to rational lattices and finite groups and to the deep relationship between these two theories. Robert L. Griess, Jr. is a professor of mathematics at the University of Michigan. His various honors include a Guggenheim Fellowship, an invited lecture at the International Congress of Mathematicians, membership in the American Academy of Arts and Sciences, and the 2010 AMS Leroy P. Steele Prize for his seminal construction of the Monster group. Rational lattices occur throughout mathematics, as in quadratic forms, sphere packing, Lie theory, and integral representations of finite groups. Studies of high-dimensional lattices typically involve number theory, linear algebra, codes, combinatorics, and groups. This book presents a basic introduction to rational lattices and finite groups and to the deep relationship between these two theories. Robert L. Griess, Jr. is a professor of mathematics at the University of Michigan. His various honors include a Guggenheim Fellowship, an invited lecture at the International Congress of Mathematicians, membership in the American Academy of Arts and Sciences, and the 2010 AMS Leroy P. Steele Prize for his seminal construction of the Monster group.|Rational lattices occur throughout mathematics, as in quadratic forms, sphere packing, Lie theory, and integral representations of finite groups. Studies of high-dimensional lattices typically involve number theory, linear algebra, codes, combinatorics, and groups. This book presents a basic introduction to rational lattices and finite groups and to the deep relationship between these two theories. Robert L. Griess, Jr. is a professor of mathematics at the University of Michigan. His various honors include a Guggenheim Fellowship, an invited lecture at the International Congress of Mathematicians, membership in the American Academy of Arts and Sciences, and the 2010 AMS Leroy P. Steele Prize for his seminal construction of the Monster group.|Rational lattices occur throughout mathematics, as in quadratic forms, sphere packing, Lie theory, and integral representations of finite groups. Studies of high-dimensional lattices typically involve number theory, linear algebra, codes, combinatorics, and groups. This book presents a basic introduction to rational lattices and finite groups and to the deep relationship between these two theories. Robert L. Griess, Jr. is a professor of mathematics at the University of Michigan. His various honors include a Guggenheim Fellowship, an invited lecture at the International Congress of Mathematicians, membership in the American Academy of Arts and Sciences, and the 2010 AMS Leroy P. Steele Prize for his seminal construction of the Monster group.