Relativistic and non relativistic quantum mechanics : both at once Currently relativistic quantum mechanics is considered an advanced topic only accessible to students who have already received considerable training in non relativistic quantum mechanics. However the authors believe that they have found an excellent pedagogic approach for simultaneously introducing both topics. This book is considered an Introductory Quantum Mechanics textbook that presents relativistic quantum mechanics to interested learners with no previous knowledge of it. The authors avoid utilization of the well known Lorentz invariant equations. Additionally they only refer to the Klein Gordon and Dirac equations to justify the use of the Poveda Poirier Grave de Peralta (PPGP) equations upon which this book is solely based (while sporadically referring to well known results obtained using the Klein Gordon and Dirac equations to avoid unnecessary complications in an introductory book). There also exist two complementary Schrödinger like and Pauli like PPGP equations the solutions of which are identical to the respective solutions of the Klein Gordon and Dirac equations associated with negative kinetic energies. These equations’ relation to the existence of antiparticles is discussed. The intended readership is undergraduate physics chemistry and engineering students with no previous knowledge of quantum mechanics as well as graduate students and professionals interested in the subject.