Metal alloys, be it based on iron, aluminium, magnesium or titanium matrix, owe their properties and performance to the assembly of phases and defects that we call the microstructure. Thermodynamic characteristics and kinetic processes on the nano- and micro-scale control the formation of the microstructure during thermomechanical treatment. The physical background of phase transformations and precipitation is studied experimentally and theoretically. Main themes in this research are the development of high-strength steel and aluminium alloys and the substitution of potentially scarce elements, for instance rare-earth metals in magnesium alloys.