Programming Language Design and Implementation (PLDI) is one of the ACM SIGPLAN's most important conferences. The precursor of PLDI was the Symposium on Compiler Optimization, held July 27–28, 1970 at the University of Illinois at Urbana-Champaign and chaired by Robert S. Northcote. That conference included papers by Frances E. Allen, John Cocke, Alfred V. Aho, Ravi Sethi, and Jeffrey D. Ullman.