The book is essentially a result of the authors' attempt to generalize Dirac's elegant method of solving the eigenvalue problem of the linear harmonic oscillator by constructing raising and lowering operators. As such, students of elementary Quantum Mechanics will find Chapters II and III quite useful and illuminating. At many stages in the book the reader will find the power of the commutator algebra unfolding in an elegant manner, as in the original Dirac approach. See the lucid application of the technique to find the eigenvalues and eigenfunctions of the Kratzer oscillator algebraically A student of Advanced Quantum Mechanics will find, in Chapter III, an illustrious application of the celebrated Infeld-Hull factorization method to find a class of ladder operators which connect the eigenstates of a hierarchy of Hamiltonians like, but not the same as, the ones in Supersymmetric Quantum Mechanics. The book will be of interest to a large spectrum of students of Physics at the Master's degree level and graduate students entering a research career in Theoretical Physics and Quantum Chemistry.