Chapter 1. Introduction.- Chapter 2. Mineralogy.- Chapter 3. Classification.- Chapter 4. Different Localities of Potassium-Rich Silica-Undersaturated Igneous Rocks and their Silica-Rich Variants.- Chapter 5. Minor and Rare Earth Element Geochemistry of K-Rich Silica- Chapter 6. Undersaturated Igneous Rocks.- Chapter 7. Chemical and Physical Constraints for Crystallization of Feldspathoids and Melilite in Potassium-Rich Rocks.- Chapter 8. Ternary Systems with Feldspathoids.- Chapter 9. Incompatible Mineral Pairs in K-Rich Rocks.- Chapter 9. Leucite- and Feldspar-Bearing Systems.- Chapter 10. Melilite- and Leucite-Bearing Systems.- Chapter 11. Phase Relations in the System Leucite-Akermanite-Albite-SiO2.- Chapter 12. P-T Stability of Phlogopite, K-Richterite and Phengite, as a Source of Potassium in the Mantle.- Chapter 13. Experimental Studies on K-Rich Rocks.- Chapter 14. Structural and Tectonic Evolution of K-Rich Silica-Deficient Volcanic Provinces of Different Continents.- Chapter 15. Genesis of Ultrapotassic Rocks.- Chapter 16. Petrologic Conclusions.- References.