Fetuin-A is a major plasma glycoprotein released mainly by the liver. Its functions include inhibition of the activity of insulin receptor, regulation of response to inflammation, inhibition of calcified matrix metabolism and ectopic mineralization, etc. Three major functional domains of fetuin-A have been identified: one similar to the Ca-binding domains, one inhibiting cysteine protease, and a domain with high affinity to insulin receptor. The fetuin-A molecule may be considered as a highly pleomorphic protein with an important impact in a variety of clinically expressed metabolic and pathological processes. It could be used as a marker in clinical practice in the future.