Klotho is a new anti-aging gene. Genetic mutation of klotho causes multiple premature aging-like phenotypes and strikingly shortens lifespan. Overexpression of the klotho gene in mice suppresses aging and extends lifespan which may involve the mechanism of suppression of insulin signaling and oxidant stress. Klotho functions as a cofactor/coreceptor regulating fibroblast growth factor (FGF) 23 signaling. Klotho acts as a glucuronidase and activates ion channel TRPV5. Klotho protects against endothelial dysfunction and regulates the production of nitric oxide. Klotho also influences intracellular signaling pathways including p53/p21, cAMP, protein kinase C (PKC) and Wnt signaling pathways. The discovery of klotho has a great impact on aging research. The purpose of this review is to provide the recent progress and future directions of klotho research. Specifically, this review will cover: klotho and aging, structure and expression of the klotho gene, localization of klotho expression, source of circulating klotho, current understanding of klotho functions, and signaling pathways of klotho.