Thymosin proteins, originally isolated from fractionation of thymus tissue, represent a class of compounds that we now know are present in numerous other tissues, are unrelated to each other in a genetic sense, and appear to have different functions within the cell. Thymosin α1 (generic drug name thymalfasin; trade name Zadaxin) is derived from a precursor molecule, prothymosin, by proteolytic cleavage, and stimulates the immune system. Although the peptide is natively unstructured in aqueous solution, the helical structure has been observed in the presence of trifluoroethanol or unilamellar vesicles, and these studies are consistent with the presence of a dynamic helical structure whose sides are not completely hydrophilic or hydrophobic. This helical structure may occur in circulation when the peptide comes into contact with membranes. In this report, we discuss the current knowledge of the thymosin α1 structure and similar properties of thymosin β4 and thymosin β9, in different environments.