I. Introduction  
A. List of Abbreviations  
B. Paper Organization  

II. Quadrature Amplitude Modulation (QAM)  
A. Evolution of QAM  
B. Various QAM Constellations  
C. Application of Different QAM Constellations in Existing Communication Systems and Standards  

III. Star QAM Constellations  

IV. XQAM Constellations  

V. HQAM Constellations  

VI. Probabilistic Shaping  

VII. Application of QAM Constellations in Wireless Communication Systems  
A. Mobile Communications  
B. Cable, Satellite, and Microwave Communications  
C. Spatial Diversity  
D. Optical Wireless Communications  
E. Miscellaneous-Emerging Areas for High Data-rate Communications  

VIII. Conclusion