This chapter begins with an analysis of the heat energy required to melt a metal for casting; here the thermal properties’ data of commonly used metals (in casting) are included. Fluidity of metals is discussed in relation to the freezing range and superheat with the aid of a sketch of the spiral-mold test. The mathematical modeling of fluidity is presented with reference to the composition factor (CF). The fluid flow system, in a casting mold, is analyzed with the application of Bernoulli’s law and useful mathematical relationships have been derived to enable a foundry engineer to correctly design a down-sprue for metal casting. The effect of pouring rate on the quality of casting is emphasized and useful mathematical models have been presented with relevant worked numerical examples. This chapter contains 15 worked numerical examples, 7 diagrams, 27 formulas/equations, and 7 MCQs with their answers given at the end of the book.