Process simulation entails the representation of a chemical process by using mathematical equations. Process simulation in Aspen Plus offers the advantages of optimizing plant performance, reducing operational costs, and improving product quality through precise modeling and analysis of chemical processes. This book was written as an educational material to help Chemical/ Environmental/Process Engineering students working on their capstone project to learn more about process design. Capstone courses are designed to help students understand process design, preliminary economic assessment and process plant optimization. The book delves into the fundamentals of process design and offers practical examples for easy understanding. This book was used with ENGR 3440, mentored research course on process design at the University of Oklahoma.