This issue of Interventional Cardiology Clinics, edited by Allen Jeremias, is devoted to Intravascular Physiology. Dr. Jeremias assembled a group of expert contributors to review the following topics: Evolution of Coronary Physiology - Basic Concepts of FFR and CFR, Concept of "Functional PCI" - The Rational for Physiologic Lesion Assessment for PCI Guidance, Limitations and Pitfalls of FFR and Adenosine-Induced Hyperemia, Evidence for the Use of FFR to Guide Clinical Decision-Making - The Landmark FFR Clinical Trials, Evaluation of Microvascular Disease and Clinical Outcomes, Hyperemic vs. Resting Indices for the Assessment of CAD, FFR for the Evaluation of Tandem and Bifurcations Lesions, Left Main, and Acute Coronary Syndromes, and CT-FFR: Basic Concept and Clinical Implementation.