Science comes with price. And with the inherent increase in research cost and technologies, scientists are continuously seeking for alternate research methodologies that are inexpensive, simple, and fast. Henceforth, fluorescence spectroscopy and microscopy offer various techniques with widespread benefits. This chapter provides an overview of the three main fluorescence tools used in molecular and cellular biology research study techniques, the theories behind them, and examples of their applications in the biological field. These are Förster (Fluorescence) resonance energy transfer (FRET), fluorescence correlation spectroscopy (FCS), and fluorescence recovery after photobleaching (FRAP).