Often when investigating new molecules, we need quick access to fundamental chemical and physical property data to anticipate a compound’s behavior under a given set of conditions. The intent of this chapter is to be that resource for researchers working with antioxidants. Common antioxidants employed in personal care formulations are presented individually. General information such as a molecule’s empirical formula, molecular weight, nomenclature, chemical abstract service (CAS) registry number, European commission (EC) number, Beilstein registry number, and simplified molecular-input line-entry system (SMILES) formula is given for each antioxidant. These are useful identifiers that are often needed when conducting research on a particular compound. SMILES is a simple way of inputting the two-dimensional layout of molecular structure into many computer databases using a simple ASCII formula. Additional chemical and physical data are provided when available, consisting of melting point, solubility, dissociation constants, pH, partition coefficient (Log P and ALOGPs), Henry’s law constant, and hydroxyl radical reaction rate constant. Partition coefficient (Log P) is experimentally determined from the ratio of concentrations of a solute in two immiscible phases (typically water and octanol), which provides the difference in solubility between the aqueous and oil phases. ALOGPS is a computer-based prediction of Log P that was developed for the pharmaceutical industry to predict properties of hypothetical molecules that are not yet synthesized. Henry’s law constant can provide similar information as Log P, especially when one of the solvent phases is gas and the other is liquid. The hydroxyl radical reaction rate constant is provided as a reference to differences between each of the antioxidants. Bear in mind, however, that in vivo the hydroxyl radical reacts so quickly that its target is often determined by its rate of diffusion. In addition, stability information is provided when available along with references to analytical methods, electron spin resonance studies, general interest articles, and skin studies.