This study takes the reader from Planck's discovery of the quantum in 1900 to interpretations and applications of non-relativistic quantum mechanics at the start of the 21st century. The introduction of the quantum idea leads off the prehistory of quantum mechanics, featuring Planck, Einstein, Bohr, Compton and de Broglie's contributions. Their original discovery papers are featured with explanatory notes and developments in Part One. The invention of matrix mechanics and quantum mechanics by Heisenberg, Born, Jordan, Dirac and Schrodinger is presented next in Part Two. Following that, in Part Three, are the Einstein-Bohr debates on the interpretation of quantum mechanics culminating in Bell's inequality and Aspect's experiment demonstrating the actuality of the long range quantum correlations to which Einstein, Podolsky and Rosen took great exception. Resolutions of quantum paradoxes and the current state of such debates are summarized. Part Four presents a selection of the most dramatic modern developments, both theoretical and experimental. These include Feynman path integrals, the modern interpretation based on decoherence, quantum optics experiments leading to teleportation, DeWitt's wave function of the universe, and a brief introduction to the end-of-the-millennium prospects of quantum computation. A concluding chapter presents the authors' conjectures for the next 100 years of the quantum.