Relativity, almost a hundred years old in its classic Einsteinian form, is one of the most fascinating threads running through science from Galileo's day to ours. This book, based on a short course at the University of Sussex, presents relativity as a natural outgrowth of dynamics: the concepts are introduced through careful physical reasoning and simple mathematics, and are then applied over a wide range, well meshed with current undergraduate syllabuses. Features* An accessible introduction through pre-Einstein relativity* Scrupulously assessed experimental evidence (mostly modern)* Elementary mathematics, aimed at a working acquaintance with kinematics, energy and momentum conservation, and the propagation of plane waves* The book includes many carefully chosen examples and student problemsIntroduction to the Relativity Principle is suitable for undergraduates studying physics, also as a preliminary to more formal courses designed for mathematicians.