The Klotho protein, also known as α-Klotho, is a multifunctional protein that regulates the metabolism of phosphate, calcium, and vitamin D. Klotho may also function as a hormone. Three Klotho protein types with potentially different functions have been identified: a full-length transmembrane Klotho, a truncated soluble Klotho, and a secreted Klotho. Recent evidence suggests that Klotho suppresses the insulin and Wnt signaling pathways, inhibits oxidative stress, and regulates phosphatase and calcium absorption.