Fractional flow reserve (FFR) is an invasive pressure-derived index of epicardial stenosis severity used in the catheterization laboratory to assess the hemodynamic significance of coronary lesions when non-invasive functional assessment has either not been performed or is inconclusive. The rationale for the use of FFR is that coronary angiography cannot accurately predict the hemodynamic significance of lesions with diameter stenosis <90% and that there is a large body of literature supporting the use of FFR for directing coronary revascularization. Specifically, in patients with stable angina and low-risk acute coronary syndromes, revascularization with either percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) surgery should be deferred for epicardial coronary stenoses with an FFR > 0.80. Use of FFR to direct coronary revascularization should continue to increase as it has been demonstrated to improve outcomes and reduce cost.