This document discusses chromophores and auxochromes in ultraviolet-visible spectroscopy. It defines chromophores as groups that absorb in the UV-visible region and undergo π → π* or n → π* transitions. Examples include ethylenic, carbonyl, and nitrile groups. Auxochromes are groups that shift absorption to longer wavelengths by extending conjugation but do not absorb themselves, such as -OH, -NH2. Bathochromic and hypsochromic shifts change the absorption maximum wavelength while hyperchromic and hypochromic effects alter absorption intensity. Woodward-Fieser rules relate conjugation in dienes to absorption maximum.