Azobenzenes are important molecular switches that can be photochemically switched between the thermodynamically more stable E-isomer and the metastable Z-isomer. Exceptions exist, in which the stabilities are reversed. They show a high thermal and photochemical stability, and the switching mechanisms are well understood. Using targeted syntheses, it is often possible to obtain certain properties. Hence, there is an increasing number of applications, such as switchable polymers including liquid crystal elastomers, molecular photomechanics, biomedical applications, 4c, 8 data storage, solar thermal fuels, and many more. For each application, the azobenzene has to be finely adjusted for its task due to two main issues. Firstly, the thermal stability of the less stable isomer can cause an unavoidable background isomerization. Secondly, the overlap of the absorption spectra of the isomers result in photostationary states (PSS) of low selectivity for either isomer at a particular wave length; this is typically compounded by wavelength dependent quantum yields.