This volume of Methods in Enzymology is concerned with the rapidly developing field of selenoprotein synthesis and its related molecular genetics. Progressive information on the topics of proteins as redox sensors, selenoproteins, and the thioredoxin system is studied using methods such as bioinformatics, DNA chip technology, cell biology, molecular genetics, and enzymology. The information on novel selenoproteins identified from genomic sequence data, as well as current knowledge on glutathione peroxidases, selenoprotein P, iodothyronine deiodinases, and thioredoxin reductases, is presented in a method-based approach.