Based on symmetry considerations, this book offers a unique derivation of the fundamental theories of physics. It first introduces all the mathematical tools the reader needs to work with symmetries in physics, assuming only basic school mathematics. These tools are then used to derive the fundamental equations of quantum mechanics, quantum field theory, electrodynamics, and classical mechanics through symmetry considerations. This enables the reader to understand the underlying assumptions and the connections between modern theories of physics. In the final part of the book, applications of the previously derived equations are discussed. The book is aimed at anyone seeking a deeper understanding of modern physics, including beginners and self-learners.