ABSTRACTRevascularization of ischemia‐producing coronary lesions is widely used in the management of coronary artery disease. However, some coronary lesions appear significant on the conventional angiogram when they are truly non–flow limiting. For this reason, it is becoming increasingly important to determine the coronary physiology. Fractional flow reserve (FFR) has emerged as a useful tool to determine the lesions that require revascularization. Measurement of FFR during invasive coronary angiography now has a class IA indication from the European Society of Cardiology for identifying hemodynamically significant coronary lesions when noninvasive evidence of myocardial ischemia is unavailable. Current data on FFR can be broadly classified into studies that compare the diagnostic accuracy of FFR measurement compared with other noninvasive modalities and studies that test treatment strategies of patients with intermediate coronary stenoses using a threshold value for FFR and that have clinical outcomes as endpoints. In this review, we will discuss the concept of FFR, current evidence supporting its usage, and future perspectives.