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.