Prof. Em. Dr. Ir. Hugo S.L.C. Hens, University of Leuven (K.U. Louvain, Belgium), taught Building Physics from 1975 to 2003, Performance Based Building Design from 1970 to 2005 and Building Services from 1975 to 1977 and 1990 to 2008. Until 1972, he worked as a structural engineer at a mid-sized architectural company, constructing houses, apartment buildings and office buildings. He has authored and co-authored over 150 articles and conference papers, and written hundreds of reports on building damage cases and their solution. He has been coordinating the international working group CIB W40 on Heat and Mass Transfer in Buildings for ten years. Between 1986 and 2008, he was operating agent of four Annexes, initiated by the International Energy Agency?s EXCO on Energy Conservation in Buildings and Community Systems: Annex 14, Annex 24, Annex 32 and Annex 41. He is also a fellow of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).