This book delves into the realm of Chemical Reaction Engineering (CRE) by showcasing the practical application of multiple-reaction stoichiometry. The authors critically assess various approaches commonly taught in undergraduate CRE courses to establish the relationships between changes in chemical species. In doing so, they propose an innovative conceptual alternative that is specifically tailored for undergraduate lectures. The book carefully selects composition measures that effectively harness the power of stoichiometric relationships in elementary reacting systems and models, which are typically covered in these courses. Going beyond the basics, it also offers a profound discussion on the value of chemical stoichiometry for tackling more intricate reaction systems and detailed models. Moreover, the book presents a simplified procedure that minimizes the reliance on complex linear algebra techniques, making the book accessible to a wider range of readers.