This chapter delves into the science behind producing high-quality metal castings for engineering applications. It focuses on the interplay between foundry technology and heat transfer during melting and solidification. The core foundry process involves pouring molten metal into a mould cavity, triggering a mechanism known as solidification, which is a liquid-to-solid phase transformation process. The solidification rate depends heavily on heat transfer within the solidifying metal, influenced by the thermal properties of both the mould and the melt itself. Understanding the thermophysical properties is crucial for controlling factors like surface quality, dimensional accuracy, and machining allowances for mass production. The chapter explores the use of sand moulds, highlighting their recyclability and cost-effectiveness, but also their limitations in terms of heat transfer. Sand moulds, compared to metal moulds, induce slower solidification due to lower thermal conductivity. The chapter then discusses energy-saving strategies in foundries, such as preheating scrap metal for melting and potentially utilizing the heat radiating from solidifying metal to preheat surrounding scrap. Finally, the chapter lays the groundwork for understanding solidification through the fundamentals of thermodynamics, thermal energy transfer during solidification, and the construction of phase diagrams for both pure metals and alloys.