1. General Introduction
2. Photoionization Equilibrium
3. Thermal Equilibrium
4. Calculation of Emitted Spectrum
5. Comparison of Theory with Observations
6. Internal Dynamics of Gaseous Nebulae
7. Interstellar Dust
8. H 11 Regions in the Galactic Context
9. Planetary Nebulae
10. Nova and Supernova Remnants
11. Active Galactic Nuclei: Diagnostics and Physics
12. Active Galactic Nuclei: Results
Appendices
Glossary of Physical Symbols
Index