The physics program at the International Linear Collider (ILC) places stringent requirements on the performance of the collider detectors. To date many of the required performance specifications have never been achieved. Furthermore, the availability of test beam facilities worldwide is becoming scarce. In this context, we are planning the ILC Detector Test Beam Workshop at Fermilab, Illinois, USA on January 17-19, 2007. This workshop will assess the current and future needs for test beams for the ILC detector R&D program, and provide input to facility managers and users, and to the World-Wide Study group for the development of a roadmap. At this workshop detector and simulation experts will describe and discuss the necessary ILC detector R&D program in view of its need for test beams. Test beam facility managers will describe the current and future test beam facilities and their availability. The workshop will provide an opportunity to evaluate the capabilities and shortcomings of existing facilities in the context of planned test beam activities. On behalf of the organizing committee we would like to ask you to inform your colleagues of the date and venue of the workshop and invite you to attend the workshop in person. If you are interested in contributing to the workshop by suggesting topics, speakers or presentations, please contact the co-chairs of the program committee - Jae Yu (jaehoonyu@uta.edu) or Felix Sefkow (Felix.Sefkow@desy.de). More information, including registration for the workshop is available at https://conferences.fnal.gov/IDTB07 Looking forward to your participation, Y.K. Kim, chair of the Local Organizing Committee.