In this book, we introduce a new Petri Net simulator called GPenSIM (General Purpose Petri Net Simulator). GPenSIM runs on MATLAB platform. GPenSIM is designed with one specific goal: allowing Petri net models to integrate with other MATLAB toolboxes. By integrating Petri net models with other toolboxes, numerous benefits can be reaped. For example, by integrating with MATLAB Fuzzy Toolbox, we can experiment with Fuzzy Petri Nets; by combining with MATLAB Control Systems Toolbox, we can create hybrid discrete-continuous systems. Hence, the main goal of this book is to introduce GPenSIM - a platform with which we can create Petri net models incorporating many other toolboxes, libraries, and functions that are already available on the MATLAB platform. There are many examples worked out in this book. These examples are simple and easy to follow. However, this book is not an introduction to Petri nets. Reader should know Petri net basics beforehand in order to start working with this book. Both the simulator GPenSIM and codes for examples (M-files) can be downloaded from the web site: http: //www.davidrajuh.net/gpensim.