The secondary hypertension chapter provides a comprehensive overview of secondary hypertension, a significant form of high blood pressure that arises due to identifiable underlying conditions, distinguishing it from primary hypertension, which has no known cause. Secondary hypertension is more frequently observed in younger populations and often presents as treatment-resistant, necessitating careful evaluation for effective management. The chapter categorizes various causes, including renal disorders, endocrine abnormalities such as primary aldosteronism and Cushing’s syndrome, and other contributors, like sleep-disordered breathing, coarctation of the aorta, and certain medications. The critical importance of accurate diagnosis is emphasized, highlighting the role of advanced imaging and biochemical tests in uncovering these underlying conditions. Treatment approaches are discussed, including lifestyle changes, targeted pharmacotherapy tailored to the specific etiology, and the consideration of surgical interventions for certain conditions, such as renal artery stenosis or adrenal tumors. Prognostic outcomes vary based on the reversibility of the underlying condition and the effectiveness of treatment strategies. For instance, conditions like pheochromocytoma may lead to significant remission of hypertension post-treatment, whereas chronic conditions require long-term management. The chapter ultimately underscores the importance of early detection of the cause of secondary hypertension, patient adherence to treatment, and continuous monitoring to prevent serious cardiovascular complications associated with uncontrolled secondary hypertension.