Laboratory Studies of X-ray Emission from Fe L-shell Transitions and Their Diagnostic Utility Gregory V. Brown High Energy Density Physics and Astrophysics Division Lawrence Livermore National Laboratory Livermore, CA 94550 Non-terrestrial objects are home to complex, dynamic, intriguing environments. High-resolution x-ray spectra from these sources measured by satellites such as the Chandra x-ray Observatory, XMM-Newton, the Solar Maximum Mission, and the soon-to-be-launched Astro-E2 provide a means for understanding the physics governing these sources. Especially rich is the x-ray emission from L-shell transitions in highly-charged iron ions. This emission is the source of a variety of diagnostics whose utility lies in the accuracy of the atomic data employed to model the x-ray spectra either globally or using ratios of key emission lines. The atomic data used to describe these diagnostics are generally provided by large theoretical calculations and benchmarked by laboratory data. I will discuss the laboratory measurements of Fe L-shell x-ray emission, past, present, and future, how these data are being implemented in spectral modeling packages, and how models are being built using data obtained exclusively in the laboratory. Work at LLNL was completed under the auspices of the US D.o.E. by the University of California Lawrence Livermore National Laboratory under contract W-7405-Eng-48 and supported by NASAs Astronomy and Physics Research and Analysis Program under work order S-06553-G.