Preparing the Foundation. Knowns and unknowns -- History and theories -- The Polarized Electorate. Ideology and polarization -- Issues and polarization -- Circumstantial evidence -- The Polarized Parties. Why are the parties more polarized? -- One-sided party polarization? -- Why are the parties polarized at all? -- Polarization and democracy -- Appendices: Five ideological series ; Regression analyses of ideological orientations.