1 Probability, Pseudoprobability, Mean Values.- 1. Introduction.- 2. Pairs of Operators.- 3. Wigners Pseudodensity.- 4. Probability Spaces.- 5. Quantum Mechanics and Fluid Dynamics.- 6. Marcinkiewicz Space and Stationary Functions.- 7. Conclusion.- 2 Local Vacua.- 1. From Bells Theorem to Where?.- 2. Some Basic Facts about Nonlocality.- 3. How to Get Rid of the Wave Function Collapse.- 4. The Physical Nature of the Local Vacuum.- 5. Diracs Covariant Vacuum as an Example.- 6. Conclusion and Outlook.- 3 Causal Quantum Theory: Why a Nonstarter?.- 1. Introduction.- 2. Formalism and Interpretation: An Example.- 3. The Copenhagen Interpretation.- 4. A Logically Possible, Empirically Viable Alternative: Causal Interpretations.- 5. A Modern Double-Slit Experiment.- 6. The Value of an Alternative Interpretation.- 7. Oposing Commitments, Opposing Schools.- 7.1. Cultural Milieux.- 7.2. The Wave-Mechanics Route.- 7.3. The Matrix-Mechanics Route.- 8. Forging the Copenhagen Interpretation.- 9. An Alternative Historical Scenario?.- 10. Internal versus External Explanations.- 4 Duality of Fluctuations, Fields, and More.- 1. Introduction.- 2. Duality of Fluctuations.- 2.1. Generalized WaveParticle Fluctuations.- 2.2. Nonclassical States.- 3. Duality of Fields.- 3.1. Classical Fields.- 3.2. Nonclassical Fields.- 3.3. The Vacuum.- 4. Duality of the Radiation Process.- 4.1. Two Kinds of Radiation Processes.- 4.2. Spontaneous Emission.- 4.3. Stimulated Emission.- 4.4. Stimulation (of Induced Emission): The BlakeScarl Experiment.- 4.5. Stimulation (of Spontaneous Emission).- 4.6. A Hypothesis.- 5. The Unobservable Wave.- 5.1. Empty Waves and Duality.- 5.2. BlakeScarl.- 5.3. Selleri and Others.- 5.4. M?ckenheim et al.- 5.5. MartinolliGozzini.- 5.6. Conclusion.- 6. Discussion: Measurement and Duality.- 6.1. Locality.- 6.2. Unitarity.- 6.3. Duality and Reality.- 5 Dualism within Dualism: Open Questions.- 6 Recent Contributions of Electron Interferometry to Wave-Particle DualitylÓ$