This is the third edition of a well‎-received textbook on modern physics theory‎.‎ This book provides an elementary but rigorous and self‎-contained presentation of the simplest theoretical framework that will meet the needs of undergraduate students‎.‎ In addition‎,‎ a number of examples of relevant applications and an appropriate list of solved problems are provided‎.‎Apart from a substantial extension of the proposed problems‎,‎ the new edition provides more detailed discussion on Lorentz transformations and their group properties‎,‎ a deeper treatment of quantum mechanics in a central potential‎,‎ and a closer comparison of statistical mechanics in classical and in quantum physics‎.‎The first part of the book is devoted to special relativity‎,‎ with a particular focus on space‎-time relativity and relativistic kinematics‎.‎ The second part deals with Schrodinger‎'‎s formulation of quantum mechanics‎.‎ The presentation concerns mainly one‎-dimensional problems‎,‎ but some three‎-dimensional examples are discussed in detail‎.‎ The third part addresses the application of‎.‎‎.‎‎.‎