This introductory book is aimed at students of engineering and material science who want to learn the necessary toolboxes of practical quantum mechanics. The authors have made sure that all the calculations are complete, and they have avoided the usage of the familiar phrase, "it can be easily shown" while being mathematically rigorous. Knowledge of the sophomore level introduction to ordinary differential equations is all that is needed. Well-designed and modern examples help the reader grasp and digest the concept before moving to the next one. The book offers a lucid exposition to the modern field of quantum computing and quantum gates, two-level systems, orbitals, spin, periodic solids, tunneling, and Fermi golden rule. The basics of electronic and optical properties of nanomaterials using the basics of quantum mechanics are presented without the reader getting lost in research articles with different notations and units. There are numerous examples in the book covering topics such as carbon nanotubes, graphene, superconducting qubits, principle of scanning tunneling microscopy, heterostructure based terahertz generation and negative differential resistance device, quantized LC circuit, Grover's search algorithm, phase kickback, quantum dots, well, nanowires, quantum of conductance, ballistic conductor, spin-orbit coupling, and spin transistor. Authors use analogies based on familiar engineering concepts wherever possible to broaden the view of the reader. The philosophy behind the book is teaching by showing how it is done and using "pictures" which is worth 1000 words.