Fractional flow reserve (FFR) has become an extremely valuable tool for assessing the hemodynamic significance of intermediate coronary lesions. This manuscript delineates the current guidelines regarding the use of FFR and discusses emerging indications for the use of this diagnostic tool and how they compare with and complement non-invasive or other invasive diagnostic modalities. The manuscript addresses some of the key unanswered questions related to FFR, the potential pitfalls of this tool and discusses future directions of use and research.