This book introduces the advanced topics regarding renal failure including manifold findings of physiologic, pathophysiologic and clinical aspects in the kidney. The kidney plays a crucial physiologic role in the regulation of urinary formation, fluid balance, nutrition metabolism, blood pressure and other aspects in the living body. Renal failure is a condition of a decline or loss of kidney function due to deficiency of functioning nephrons. Acute renal failure is a syndrome, which is characterized by acute decline or loss of kidney function due to temporary disfunctioning or blocking of nephrons. Acute renal failure is a reversible condition and is a secondary manifestation, a complication of another underlying critical illness. Chronic renal failure is a condition of slow, gradual decline of kidney function due to irreversible destruction of nephrons. This book provides recent information concerning acute and chronic renal failure in clinical aspects, and is constituted in five chapters.