Selenoproteins are a group of proteins that contain the trace element selenium in the form of the amino acid selenocysteine. These proteins play important roles in various biological processes, including antioxidant defense, thyroid hormone metabolism, and immune response. Selenoproteins are essential for human health, and deficiencies in selenium can lead to serious health conditions such as Keshan disease and Kashin-Beck disease. Research in the field of selenoproteins aims to understand their functions, regulation, and potential health benefits, as well as how selenium levels and selenoprotein expression may be linked to disease states.