  Vertex algebras and factorization algebras are two approaches to chiral
conformal field theory. Costello and Gwilliam describe how every holomorphic
factorization algebra on the plane of complex numbers satisfying certain
assumptions gives rise to a Z-graded vertex algebra. They construct some models
of chiral conformal theory as factorization algebras. We attach a factorization
algebra to every Z-graded vertex algebra.
