Most organic molecules have as the lowest electronic energy state a singlet, S0, characterized by paired electrons and known as the ground state. Excited states include singlets, called Sn, and triplets, called Tn, which have two unpaired electrons. Each electronic state corresponds to a different electronic distribution, mainly influencing a molecule’s physical and chemical properties. As a result, each excited state can be seen as a different molecule. Physical properties—such as dipole moment, geometry, and bond lengths—and chemical properties—like acidity and reactivity—often change significantly from the ground state to the first excited state. Emission and excitation spectra result from radiative transitions between S1 and S0 (fluorescence) and T1 and S0 (phosphorescence). These concepts also apply to inorganic compounds. In such systems, however, excited states can display a broader range of spin multiplicities, including doublets, quartets, quintets, and higher multiplicities. In cultural heritage studies, we analyze various materials. The past decade has brought significant progress in understanding them. As shown in this book, molecular luminescence has played a key role in studying pigments and dyes, using microspectrofluorimetry and portable spectrofluorimeters. The field of chemometrics has expanded, broadening our capabilities and allowing exploration into new areas. It enables the use of spectra without correction, fostering innovative research and discoveries.