The goal of this book is to provide the reader on how to design a structure and to implement a first version of a model library as well as to develop basic models for the transient simulation of Combined Heat and Power plants (CHP).As the CHP plant consists of many different components, modular approach and top-down design has been implemented in the model library development. Solid base for the project is defined which are including project rules for modeling the components (e.g. robustness and reusability), default library structure arrangement and model documentation. Later development is obliged to strictly follow the rules and concepts introduced during this stage in order to minimize the mistakes in modeling, easier understanding of the project and models as well as to provide an organized environment for CHP plant modeling. By taking advantage of the modular design of this CHP library, planning and analysis of CHP plant can be simulated easily by using drag-and-drop method while parameters in models should be defined according to the target CHP plant.