Kenneth R. Ludwig was born in 1944 in Berkeley, California. He received his B.S. (Chemistry, 1965), M.S. (Geology, 1967) and Ph.D. (Geochemistry, 1973) degrees all from the California Institute of Technology. He worked for the U.S. Geological Survey from 1973 to 1995, when he was recruited by the BGC to found a uranium-decay dating program. Ludwig served as Director and President of BGC from 2000 to 2003. Ludwig is singular among geochronologists as being expert in both the uranium-lead and uranium series methods. He is widely recognized for major contributions to understanding isotope systematics that have enabled improved accuracy and precision, for devising optimal analytical strategies, and providing mathematically rigorous tools for data interpretation. Ludwig’s public domain software package ISOPLOT is used in more than 100 isotope geochemistry labs worldwide. His more recent SQUID software for ion microprobe data analysis is also used internationally.