th The Who Who in Fluorescence 2009 is the 7 volume of the Who who series. The previous six volumes (2003 – 2008) have been very well received by the fluorescence community, with 1000 of copies being distributed around the world, through conferences and workshops, as well as through internet book sites. In addition, the Institute of Fluorescence (http://theinstituteoffluorescence.com/) mailed 100 of copies of the 2008 volume to contributors around the world. This new 2009 volume features some 419 entries from no fewer than 41 countries worldwide, as compared to 418 entries (38 different countries) in 2008 and 405 entries in the 2007 volume, respectively. We have received 29 new entries this year, and deleted 25 entries that were not updated by contributors from past years. In 2008, 129 AIM numbers were submitted as compared to 106 in 2007. This year the number has risen again to 136 AIM numbers submitted. This year we also see the introduction of the h-index number listing, a publication statistic provided by the Thompson ISI Web of Science. Some 42 contributors provided their h-numbers. In 2009 we also see a continued and strong company support, in light of the current world economic climate, which will enable us to further disseminate the volume in 2009– 2010. In this regard we especially thank the instrumentation companies for their continued support, where without their financial contributions, it is likely that the volume would not be the success it is today.