Take any combination of the following features: supramolecular structures with a specific fluorescent probe localized as you would like; nanoscale spatial reso- tion; tailor-made molecular and/or solid-state fluorescing nanostructures; us- friendly and/or high- throughput fluorescence techniques; the ability to do wh- ever you wish with just one single (supra)molecule; utilization of non-linear optical processes; and,last but not least,physical understanding of the processes resu- ing in a (biological) functionality at the single molecule level. What you will then have is some recent progress in physics,chemistry,and the life sciences leading to the development of a new tool for research and application. This was amply demonstrated at the 8th Conference on Methods and Applications of Fluorescence: Probes,Imaging,and Spectroscopy held in Prague,the Czech Republic on August 24th–28th, 2003. This formed a crossroad of ideas from a variety of natural science and technical research fields and biomedical applications in particular. This volume – the third book in the Springer-Verlag Series on Fluorescence – reviews some of the most characteristic topics of the multidisciplinary area of fluorescence applications in life sciences either presendted directly at th 8th MAF Conference or considered to be a cruical development in the field. In the initial contribution in Part 1 – Basics and Advanced Approaches,the - itors explain the basics of fluorescence and illustrate the relationship between some modern fluorescence techniques and classical approaches. The second contrigution by B.