Förster resonance energy transfer (FRET), along with the association of recent advancements in optical techniques like confocal and two-photon microscopy, facilitates the measurements of two-dimensional spatial distribution in steady state as well as dynamic bimolecular interactions, providing a way to understand different biological systems at molecular level with a detailed mechanism. Since past couple of decades, FRET became an exceptional and important fluorescence-based technique due to its potential advantages at nanometer scale. In particular, FRET brings more insight towards the structure-function correlation. In this chapter, the application of FRET in the field of protein chemistry and their interactions with other biological molecules (protein, carbohydrate, drug, and drug) are more emphasized along with the basic principles of FRET.