Refining phenomena of Basic oxygen steel-making processes are very complex with hazardous features due to simultaneous metal-metal, slag-metal, metal-gas, slag-gas, and various chemical reactions at high temperatures.The Steel-making process has been continued since 1847; till now, it is very challenging to predict the transient metal, slag, and gas compositions and temperature during 15-20 minutes of refining time. It also involves controlling process parameters such as hot metal charging, scrap charging, flux charging, lance height, and oxygen flow rate. Along with these parameters, minimizing energy cost, maximizing yield, and reducing environmental pollution are current concerns. In this book, a dynamic mathematical model has been developed to account for such interconnected phenomena.