Material balances are important when designing a new process or analyzing an existing one. They are approximately at all times prerequisite to all other calculations in the solution of process engineering problems. They are used in the industry to calculate mass flow rates of different streams entering or leaving chemical or physical processes. In this chapter, the concept of material balance as it is related to chemical processes is introduced. The material balance for a general system and highlights on its importance in the analysis of chemical engineering processes are illustrated. Further, the difference between systems in terms of their operation mode, that is, steady or unsteady state, and open or closed, is defined. How to solve the steadystate material balance in a single-unit process with no chemical reactions is explained. The following highlights the focal learning objectives that should be achieved toward the end of this chapter.