This thesis explores the role of coronary physiology in the diagnosis, management, and prognosis of chronic and acute coronary syndromes. Part A focuses on the procedural considerations of assessing coronary physiology invasively using pressure and flow measurements. The authors discuss the limitations of resting indices in evaluating coronary stenosis severity and the importance of performing physiological assessments meticulously. Moreover, they investigate the comprehensive diagnosis of chronic coronary syndromes and the insights provided by combined pressure and flow measurements. Also, the impact of percutaneous coronary intervention (PCI) on resolving myocardial ischemia in discordant stenoses based on the novel coronary-flow-capacity (CFC) concept is assessed. Part B focuses on microvascular function in acute coronary syndromes, particularly in patients with ST-segment elevation myocardial infarction (STEMI). The authors discuss the pathophysiology, diagnostic armamentarium, and treatment strategies related to microvasculature in patients with STEMI. They investigate the microvascular function in the acute event of myocardial infarction and how it restores following a successful primary percutaneous intervention. Overall, the thesis provides a comprehensive overview of the role of the coronary microcirculation in the diagnosis, management, and prognosis of chronic and acute coronary syndromes. The authors emphasize the importance of performing physiological assessments meticulously and highlight the limitations and challenges associated with current diagnostic methods. They also provide insights into the potential future directions for the field.