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 problems Introduction to the Relativity Principle is suitable for undergraduates studying physics, also as a preliminary to more formal courses designed for mathematicians.