Xcos is a very powerful and open source block-based modeling and simulation system for dynamical systems. Its capabilities are comparable to commercially available block-based modeling and simulation tools, including Simulink®, one of the most popular commercial tool. Xcos is useful for modeling continuous and discrete dynamical systems. Further, it provides facilities to seamlessly integrate continuous and discrete components in a single model, making it capable to handle hybrid dynamical systems. Xcos provides a modular approach to model complex dynamical systems using a block diagram editor. Xcos contains a rich library of commonly used blocks, arranged in various palettes for the convenience of searching them, for elementary operations needed to construct models of many dynamical systems. These blocks can be dragged and dropped into the model editor to create a simulation model. For advanced users, Xcos provides facilities to create new blocks and to create their own libraries to further extend the capabilities of Xcos. Since Xcos is available free of cost to everyone across the globe and is continuously upgraded by a strong team of open source developers, it is suitable for all undergraduate students, researchers, professors and professionals in any field of Science and Engineering. Further, many commercial developers are also using it to reduce their project cost and has reported many successful applications. The basic objective to write this book is to teach Xcos in a friendly, non-intimidating fashion, without any previous modeling experience. Therefore, the book is written in simple language with many sample problems in mathematics, science, and engineering. Starting from the basic concepts, the book gradually builds advanced concepts, making it suitable for freshmen and professionals. The Xcos models of all the examples included in this book are available at https://github.com/arvindrachna/Introduction_to_Xcos. There are a few books available for teaching basic concepts of Xcos, which is the basic motivation to write this book. We hope the book will be helpful to spread the awareness and use of Xcos for modeling dynamical systems. The book consists of fifteen chapters. The first chapter gives a brief introduction to dynamical systems and Xcos modeling environment. The second chapter describes the Sources Palette, which consists of blocks to generate varieties of signals and data for models. The third chapter describes the Sink Palette, which consists of different signal and data visualization blocks. The fourth chapter describes the Mathematical Operations Palette, which consists of blocks implementing different mathematical operations and functions. The fifth chapter describes the Matrix Operation Palette, which is a collection of blocks for various matrix operations. The sixth chapter describes the Signal Routing Palette, which consists of blocks to route signals among blocks. The seventh chapter describes the Event Handling Palette, which consists of blocks for handing events during simulation. The eighth chapter describes the Integer Palette which consists of blocks to perform various Boolean operations and bit manipulation operations.