Fluorescence techniques enjoy ever-increasing interest from a multitude of disciplines: physics, chemistry, biology, geology, pharmacology, toxicology and medicine. Besides widespread fundamental and applied research of fluorescence in university laboratories, one observes a substantially enhanced effort by smaller and larger companies towards the development of new fluorescence-based diagnostic tools. This increased use of fluorescence techniques is greatly enhanced by the improved instrumentation, in particular that of microscopic imaging, such as confocal scanning and multi-photon excitation microscopies. Moreover, the development of many new molecular probes with higher selectivity for specific micro-environmental properties has stimulated many new researchers to employ fluorescence techniques. This topic book, the second in the Springer Series on Fluorescence, reflects this exciting scientific progress and deals, among others, with new approaches and new probes in fluorescence spectroscopy, single molecule fluorescence, applications in biomembrane and enzyme studies and imaging of living cells.