This is the fourth volume in the Reviews in Fluorescence series. To date, three volumes have been both published and well received by the scienti c community. Several book reviews in the last few years have also favorably remarked on the series. In this fourth volume we continue the tradition of publishing leading edge and timely articles from authors around the world. We thank the authors for their timely and exciting contributions. We hope you nd this volume as useful as past volumes, which promises to be just as diverse with regard to uorescence-based content. Finally, in closing, I would like to thank to Aaron Johnson, formerly at Springer, for helping me to publish this book serial over the last four volumes. Thanks also go to Michael Weston at Springer for help in publishing this current volume. Baltimore, Maryland Chris D. Geddes v Contents Simple Calibration and Validation Standards for Fluorometry ...1 Ute Resch-Genger, Katrin Hoffmann, and Dietmar Pfeifer Membranes and Fluorescence Microscopy...33 Luis A. Bagatolli Electronic Energy Transport and Fluorescence Spectroscopy for Structural Insights into Proteins, Regular Protein Aggregates and Lipid Systems ...53 ? ? Therese Mikaelsson, Radek Sachl, and Lennart B. -A. Johansson Spectra FRET: A Fluorescence Resonance Energy Transfer Method in Live Cells...87 Ekaterina A. Bykova and Jie Zheng Boronic Acid Based Modular Fluorescent Saccharide Sensors...103 John S. Fossey and Tony D. James Fluorescence Solvent Relaxation in Cationic Membranes ...