Hubert Irwin Aaronson (Hub) received his BS, MS, and Ph.D. in metallurgical engineering at Carnegie Institute of Technology, Pittsburgh, Pennsylvania (now Carnegie Mellon University). He was a worldwide leader in the field of phase transformations of metals and alloys for more than half a century. He published more than 300 technical papers, organized numerous symposia and conferences, served a number of technical committees, and was recognized with many awards. He was a member of the U.S. National Academy of Engineering, Washington, District of Columbia; a fellow of both The Minerals, Metals and Material Society and ASM International; and an honorary member of the Japan Institute of Metals, Sendai, Japan. As R.F. Mehl Professor Emeritus at Carnegie Mellon University, Hub continued his professional activities to the very end until his passing in December 2005.