I. Introduction 893 A. The Drug Discovery Process 895 B. Characteristics of Privileged Substructures 896 C. Scope of the Review 897 II. Phenyl-Substituted Monocycles 898 A. Biphenyls 898 B. Arylpiperidines 899 C. Arylpiperazines 901 D. 1,4-Dihydropyridines 901 E. Dihydropyrimidones 902 III. Fused [7−6] Ring Systems 904 A. 1,4-Benzodiazepin-2-ones 904 B. 1,5-Benzodiazepin-2-ones 905 C. 1,4-Benzodiazepin-2,5-diones and Pyrrolo-[2,1-c][1,4]benzodiazepin-5,11-diones 906 D. 1,4-Benzothiazepin-5-ones 907 E. 5,11-Dihydro-benzo[e]pyrido[3,2-b][1,4]diazepin-6-ones 907 IV. Fused [6−6] Ring Systems 908 A. Benzopyrans, Chromones, Coumarins, and Pyranocoumarins 908 1. Benzopyrans 908 2. Chromones 909 3. Coumarins 911 4. Pyranocoumarins 911 B. Quinoxalines/Quinazolines 913 1. 3,4-Dihydroquinoxalin-2-ones (Benzopiperazinones) 913 2. Quinazolinones 915 3. Quinazolindiones 916 4. Imidazoquinoxalines 917 V. Fused [5−6] Ring Systems 919 A. Indoles 919 B. Benzimidazoles 921 C. Benzofurans 922 D. Benzothiophenes 924 VI. Conclusions 925 VII. Acknowledgments 925 VIII. References 925