In the early period of the theory of valency, difficulty was felt in explainingMolecular compounds “molecular compounds” formed by the addition of species to molecules in which the valenceValence (valency) was completely saturated. Common examples of these were produced through the reaction of metal salts with ammoniaAmmonia to give metal-ammine compounds. Attempts to understand such metal-amminesMetal-ammines date back to the first half of the nineteenth century, with a leading theory introduced by Christian BlomstrandBlomstrand, Christian (1826–1897) in 1869. Blomstrand’s chain theoryChain theory was later extended and modified by Sophus JorgensenJorgensen, Sophus Mads (1837–1914) from 1878 onwards. Joining these efforts was Alfred WernerWerner, Alfred (1866–1919), who after studying the stereoisomerism of trivalent nitrogen in his 1890 doctoral dissertation, presented hisWerner coordination theory coordination theoryCoordination theory in 1893, a radical departure from the previous Blomstrand-Jorgensen chain theoryBlomstrand-Jorgensen chain theory. Not only did coordination theory better correlate the properties of compounds based on their composition and configurationConfiguration, but Werner’s proposed structures also introduced the first understanding of stereoisomersStereoisomers in metal complexes. While initially disputed by Jorgensen, Werner’s theory finally displaced the older chain theoryChain theory and resulted in the awarding of the Nobel PrizeNobel Prize in Chemistry to Werner in 1913. The life and career of Werner is presented with a focus on his coordination theoryCoordination theory and its introduction of stereoisomersStereoisomers in metal complexes.