In routine clinical practice, a sizeable proportion of patients with suspected coronary artery disease (CAD) undergo coronary angiography without prior non-invasive functional evaluation. In this situation, the decision wheter to perform revascularization is taken solely on the basis of angiographic parameters, which are often limited in assessing the lesions that are functionally significant and ultimately responsible for patients' symptoms. Fractional flow reserve (FFR) is a validated method for assessing hemodynamic significance of coronary stenoses based on the use of pressure wires and assessment of hyperemic pressure gradients across coronary lesions. FFR can guide clinical decision making in several anatomical settings: e.g. intermediate stenosis, left main stenoses, multivessel disease, bifurcation lesions. Treatment strategies guided by FFR have been shown to be equally safe and more efficacious than angiography-guided PCI. FFR is readily available in the catheterization laboratory, and can be easily measured during coronary angiography. FFR represents a unique tool for interventional cardiologists to combine anatomical and functional information, allowing the selection of optimal revascularization strategy in patients with CAD.