1. Introduction. 2. Classification of Humic Acids. 3. Spectroscopic Characteristics of Humic Acids and Fulvic Acids. 4. P Type Humic Acids. 5. Elementary Composition of Humic Acids and Fulvic Acids. 6. Humus Composition of Soils. 7. Analysis of A0 Horizon. 8. Model Experiments on the Formation of Humic Acids. 9. Chemical Properties of Various Types of Humic Acid. 10. The Nature and Genesis of Humic Acid. 11. Diagensis of Humus. 12. Complementary Remarks. References. Index.