Analytical measurements at the single molecule level under ambient conditions have become almost routine in the past few years. The application of this technology to fundamental studies of heterogeneity in biomolecular structure and dynamics, chemical and biological reaction kinetics, andphotophysics provides a rich playground for molecular scientists. The potential use of single molecule detection for nanotechnology and quantum information processing is a new and almost unexplored area. This handbook is intended for those interested in a practical introduction to single molecule investigations using fluorescence techniques and places special emphasis on the practicalities of achieving single molecule resolution, analysing the resulting data and exploration of the applications inbiophysics. It is ideal for graduate research students and others embarking on work in this exciting field.