Single molecule tools have begun to revolutionize the molecular sciences, from biophysics to chemistry to cell biology. They hold the promise to be able to directly observe previously unseen molecular heterogeneities, quantitatively dissect complex reaction kinetics, ultimately miniaturize enzyme assays, image components of spatially distributed samples, probe the mechanical properties of single molecules in their native environment, and "just look at the thing" as anticipated by the visionary Richard Feynman already half a century ago. Single Molecule Tools, Part A: Fluorescence Based Approaches captures a snapshot of this vibrant, rapidly expanding field, presenting articles from pioneers in the field intended to guide both the newcomer and the expert through the intricacies of getting single molecule tools.