Part I Introduction.- The character of a scientific theory.- Field Theories and Variational approach.- Fundamental Principles and Field Theories.- Exercises.- Part II Special Relativity.- Motivations.- Mathematical model.- Electromagnetism in SR.- Exercises.- Part III General Relativity.- Motivations.- Lagrangian formulation of GR.- Applications.- Exercises.- Part IV Beyond Relativity.- Motivations.- Theory and Experiments.- Exercises.