Our current understanding of the basic building blocks of matter and interactions between them is called the Standard Model of Particle Physics (SM). This most fundamental description of Nature incorporates three of the four basic interactions which govern how the Universe works, the electromagnetic, weak and strong interactions. This unit investigates the mathematical underpinnings of the SM, a quantum field theory constructed upon fundamental notions of symmetry including Lorentz and local gauge invariance. It also explores the notion of spontaneous symmetry breaking, the Higgs field and the way that fundamental particles acquire mass. The interplay between theory and experiment, which has driven the SM's development, is highlighted. Finally, limitations of the model and possible extensions which could overcome them are discussed. You will learn how the SM is constructed based on symmetry principles, quantum fields and their space-time derivatives; how to derive equations of motion for the fields using the Action Principle; and how predictions for physical observables such as cross sections and decay rates can be calculated starting from the SM Lagrangian density. By studying examples of both recent and historically significant measurements confirming or challenging the SM, you will gain experience in reading and interpreting the scientific literature. Through this unit you will develop an appreciation of humankind's most contemporary and successful attempt to describe Nature in terms of fundamental laws.