This lecture covers the fundamentals of phase transformations, focusing on solidification. Topics include thermodynamics of mix energy, calculation of mix entropy, mix enthalpy, nucleation, dendritic growth, eutectic solidification, and constitutional supercooling. The instructor discusses the controlled solidification process, dendritic structure, pearlite formation in steels, and the growth of a cellular structure. The lecture also explores the series of nanosecond time-resolved bright field images and diffraction patterns revealing solidification processes after laser melting.