Abstract. Background: Increased renal sodium avidity is a hallmark feature of the heart failure syndrome. Summary: Increased renal sodium avidity refers to the inability of the kidneys to elicit potent natriuresis in response to sodium loading. This eventually causes congestion, which is a major contributor to hospital admissions and mortality in heart failure. Key Messages: Important novel concepts such as the renal tamponade hypothesis, accelerated nephron loss, and the role of hypochloremia, the sympathetic nervous system, inflammation, the lymphatic system, and interstitial sodium buffers are involved in the pathophysiology of renal sodium avidity. A good understanding of these concepts is crucially important with respect to treatment recommendations regarding dietary sodium restriction, fluid restriction, rapid up titration of guideline-directed medical therapies, combination diuretic therapy, natriuresis guided diuretic therapy, use of hypertonic saline, and ultrafiltration.