This book is a supplementary textbook in Theoretical Mechanics with an introduction to Lagrange’s equations and Hamiltonian theory. Theoretical l Mechanics practically originated from Newton’s famous book about fundamentals of physics and developed gradually until now. Like any other books of Schism’s series, this book starts every chapter with concise summary explanation of pertinent concepts (definitions, laws and theorems) - then solves typical graded problems and at the end of the chapter introduces similar supplementary problems as exercises for students! It has totally 720 solved problems that are common problems of most examinations. Therefore this book is very useful for students who are getting ready for an examination in the least possible time! Most important topics of this book are: fundamental concepts and principals of Newtonian mechanics like Newton’s laws of motions , systems of particles, space motion of rigid bodies, Lagrange’s and Hamiltonian equations and some facts about astronomy.