The Hahn-Hellinger Theorem.- The Spectral Theorem for Unitary Operators.- Symmetry and Denseness of the Spectrum.- Multiplicity and Rank.- The Skew Product.- A Theorem of Helson and Parry.- Probability Measures on the Circle Group.- Baire Category Theorems of Ergodic Theory.- Translations of Measures on the Circle.- B. Host's Theorem.- L∞ Eigenvalues of Non-Singular Automorphisms.- Generalities on Systems of Imprimitivity.- Dual Systems of Imprimitivity.- Saturated Subgroups of the Circle Group.- Riesz Products As Spectral Measures.- Additional Topics.- Calculus of Generalized Riesz Products.