This book covers the major theories of non-uniform cellular automata that have been developed during the last four decades. The non-uniform cellular automata started their journey as an effective tool of generating pseudo-random numbers in hardware. Over the years, they have flourished in different directions and the theories, related to reversibility, number conservation, maximality, cycle structure, convergence, chaos, etc. have been developed. The theories are presented, in this book, followed by the examples with pointers to the applications for better understanding. The readers can discover new application areas where the theories, provided in this book, are suitable. A few open problems are also included to trigger a reader to undertake research on non-uniform cellular automata to address the problems. The content of this book also meets the needs of undergraduate and graduate students who opted for the course on cellular automata.