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Article Contents

ABSTRACT

1.INTRODUCTION
1.1.H II Regions in the Context of the ISM
1.2.Environments and Systematics
1.3.Internal Structure
1.4.Ionizing Clusters

2.METHODS OF ABUNDANCE DETERMINATION
2.1.The "Conventional" (Direct) Method
2.2.Nebular Models
2.3."Bright-Line" Methods

3.ABUNDANCE GRADIENTS IN GALACTIC DISKS
3.1.The Phenomenon
3.2. Trends with Galaxy Type
3.3.Elements other than Oxygen
3.4.Comparison with the Galactic Abundance Gradient
3.5.Comparison with Chemical Evolution Models

4.ABUNDANCES IN METAL-POOR DWARF GALAXIES
4.1.Nomenclature
4.2.The "I Zw 18 Problem" and the Mass-Metallicity Relation
4.3.Dwarf Galaxies as Tests of the Simple Model
4.4.Dwarf Galaxies and the Extragalactic H II Region Sequence
4.5.Elements other than Oxygen

5.HELIUM ABUNDANCES AND THE PRIMORDIAL COMPONENT
5.1.Cosmological Motivation
5.2.Demands on the Observations
5.3.Current Status and Future Prospects

6.SOME OUTSTANDING ISSUES

7.FUTURE PROSPECTS

REFERENCES