My aim in this general talk will be to air some questions, rather than offer firm answers, because the most basic questions about galaxies are indeed still unresolved. In particular:
1. We do not know why such things as galaxies should exist at all — why these assemblages of stars and gas with fairly standardised properties are the most conspicuous large-scale features of the cosmos.
2. About 90% of the mass associated with galaxies is hidden. The luminous stars and gas contribute only about a tenth of the gravitating material inferred from dynamical arguments. What the rest consists of is still a mystery.
3. It is unclear why the nuclei of some galaxies flare up, and release the colossal amount of non-stellar radiation emitted from quasars and radio galaxies, as discussed by Maarten Schmidt in his discourse.