The property profile of modern alloys is determined by their microstructureMicrostructure, based on the chemical composition; the morphologyMorphologies, distribution and quantity of the phases; and the process history of the material. Melting, casting, and solidificationSolidification are the starting points in classical alloy production. At known composition, phase diagramsPhase diagram can help to predict the phases present as a function of temperatureTemperature under equilibrium conditions. However, during melting, alloying, casting, and solidificationSolidification, equilibrium conditions are rarely encountered. Similar can be said about heat treatments and wrought processing. It can therefore be helpful to take a closer look at these dynamic processes to optimize processing steps and properties. In situIn situ investigations using synchrotron radiation focusing on the solidificationSolidification behavior of magnesium alloys clearly show the influence of solidificationSolidification parameters on the formation and transformation of stable and metastable phases. This information can contribute to validate and/or to improve phase diagramsPhase diagram and suited predictions.