Inhaltsangabe1. Introduction.- 2. Schrödinger Theory from the Perspective of 'Classical' Fields Derived from Quantal Sources.- 3. Quantal Density Functional Theory.- 4. The Hohenberg-Kohn Theorems and Kohn-Sham Density Functional Theory.- 5. Physical Interpretation of Kohn-Sham Density Functional Theory.- 6. Quantal Density Functional Theory of the Density Amplitude.- 7. Quantal Density Functional Theory of the Discontinuity in the Electron-Interaction Potential Energy.- 8. Further Insights Derived Via Quantal Density Functional Theory.- 9. Epilogue.- Appendices.- A. Proof of the Pure State Differential Virial Theorem.- B. Proof of the Harmonic Potential Theorem.- C. Analytical Expressions for the Properties of the Ground and First Excited Singlet States of the Hooke's Atom.- D. Derivation of the Kinetic-Energy-Density Tensor for Hooke's Atom in Its Ground State.- E. Proof of the S System Differential Virial Theorem.- F. Derivation of the Pair-Correlation Density in the Local Density Approximation for Exchange.- References.