The late Harlan D. Mills was widely recognized for his contributions as a mathematician concerned with bringing more rigor into systems and software development. At the time of his death in 1996, he was the Director of the Information Systems Institute in Vero Beach, Florida. He had previously worked at IBM from 1964 to 1987, where he achieved fellow status. While at IBM, he served as Director of Software Engineering and Technology for the Federal Systems Division, and a member of the IBM Corporate Technical Committee. Harlan Mills taught at the University of Maryland, Iowa State, Princeton, John Hopkins, and New York universities. Mills was a mathematician and a software engineering pioneer, known as the originator of clean-room technology transfer and the chief programmer team concept. Mills believed that programs were rules for mathematical functions. He applied incremental development and statistical theory to software testing, which led to the technology of statistical usage testing and quality certification. He was known for integrating mathematical and statistical principles with engineering technologies, which led to the achievement of error-free software. This process is used in North America and Europe to design reliable software from medical devices to nuclear power plant controls and telephone switch components.