UV-vis spectroscopy is an inexpensive, simple, flexible, non-destructive, analytical method appropriate for a wide class of organic compounds and some inorganic species. UV-vis spectrophotometers measure the absorbance or transmittance of light passing through a medium as a function of the wavelength. Chemical engineers apply it for quantitative analysis, to derive liquid phase reaction kinetics, and to identify the mechanism at the molecular scale. High performance liquid chromatography and ultra-high performance liquid chromatography integrate UV-vis detectors to identify and quantify the concentration of compounds in liquid streams. Combining these techniques with mass spectrometry facilitates identifying all species. UV-vis diffuse reflectance spectroscopy is a variant with enhanced scattering properties that measures the properties of solids and powders. A bibliometric analysis of the 10 000 most cited papers referring to UV-vis (2016 and 2017) groups research in four major clusters: nanoparticles and nanostucutres; photocatalysis and water treatment; crystals, complexes, and derivatives; and Ag and Au nanoparticles biological interaction.