Kidney has one of the major regulatory and excretory functions. Nephron is the functional unit of kidney with following sites. The proximal convoluted tubule (PCT) reabsorbs 100% glucose, 85% sodium bicarbonate, 65% of sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg). Classification of diuretics based on site of action and efficacy. A detailed discussion on high-efficacy/high-ceiling-loop diuretics, medium-efficacy diuretics, and low-efficacy diuretics has been presented in this chapter with the help well-illustrated figures which are self-explanatory. At the end of this chapter there are 26 questions along with their crisp and to the point answers have been also given, which will be of benefit for answering the short answers and even a viva voce question.