Metals and alloys establish modern infrastructure and technology, driving innovation and efficiency across diverse applications. Metals are elemental substances known for their conductivity, malleability and durability, essential in construction, electronics and transportation. Alloys are mixtures of metals or metals with non-metallic elements with enhanced properties like strength, corrosion resistance and specialised functionalities such as magnetism. Phase transformations are critical phenomena in materials science, involving changes in the microstructure of substances due to variations in temperature, pressure or chemical composition. These transformations fundamentally alter material properties, impacting their mechanical, electrical and magnetic behaviours. Understanding phase transformations is essential for designing and manufacturing advanced materials with desired characteristics. This knowledge enables the optimization of material properties for specific functional requirements, ensuring technological advancements and innovation in various industries. This book is a valuable compilation of topics, ranging from the basic to the most complex theories and principles in the field of phase transformation. The topics covered in this extensive book deal with the core subjects of material science. It will serve as a reference to a broad spectrum of readers.