The 5th edition of Model Building in Mathematical Programming by H. Paul Williams delves into the general principles of model building in mathematical programming, illustrating how these principles can be applied through simplified yet practical problems from diverse contexts. The book offers suggested formulations and solutions alongside computational experience to provide insight into the challenges of solving such models. By focusing on the importance of both building and interpreting models rather than just their solution processes, Williams aims to bridge a gap left by many other works that focus primarily on algorithmic aspects. This edition has been updated to maintain its relevance and popularity, offering new insights and continued guidance for those interested in mathematical programming.