Written by two veteran environmental modelers, this textbook is about quasi-realistic models in the atmospheric and oceanic sciences, which have become an indispensable tool. Understanding the basis and limitations of these models is important since far-reaching decisions about the environment are based on these models. The book describes what these models are, what they are based on, how they function, and then, most innovatively, how they can be used to generate new useful knowledge about the environmental system. This generation of knowledge by computer models is discussed from an epistemological perspective and illustrated by numerous examples from applied and fundamental research. Illustrated by numerous examples, from both applied and fundamental research, the text includes ample technical appendices and is a valuable source of information for graduate students and scientists alike working in the field of environmental sciences.