A sequence of four lectures outlines the physical and mathematical foundations of relativity, beginning with the experiential roots of space and time and the operational role of clocks and reference bodies. It treats special relativity through the relativity of simultaneity and Lorentz transformations, then introduces the equivalence principle and a geometric description of gravitation in which the metric tensor and spacetime curvature replace Newtonian force. The presentation develops the tensor formalism that yields the field equations, examines limiting cases and practical applications, and derives observable consequences such as corrections to planetary motion and the deflection of light.