Molecular switches based on E/Z photoisomerization have been used in different contexts in order to control a variety of processes in different systems, from peptide conformation control to molecular data storage devices, from catalysis to smart materials. The syntheses, properties and applications of several types of E/Z photochemical switches are presented with special attention paid to azobenzenes, overcrowded alkenes and switches based on the protonated Schiff base chromophore of rhodopsins.