This chapter contains sections titled: Introduction Directing and Activating Effects of the Azo Group General Considerations Reactions of Aromatic Side-chains The Phenylazo Substituent The Arylazo Substituent Transmission of Resonance Effects through the Azo Group Electrophilic Aromatic Substitution Reactions in Azo Compounds General Considerations Reactions Other Aromatic Substitution Reactions Nucleophilic Aromatic Substitution Free-radical Substitution Miscellaneous Substitutions Nuclear Magnetic Resonance Spectra of Azo Compounds The Protonated Azo (Azonium) Group as a Substituent Directing and Activating Effects of the Azoxy Group General Considerations Reactions of Aromatic Side-chains Electrophilic Substitution Reactions in Azoxy Compounds General Considerations Substitution in Alkylazoxybenzenes Azoxybenzene and Substituted Azoxybenzenes The Activating Power of the Phenylazoxy Group Other Aromatic Substitution Reactions Nucleophilic Aromatic Substitution Miscellaneous Substitutions Nuclear Magnetic Resonance Spectra of Azoxy Compounds Aliphatic Compounds Aromatic Compounds Directing and Activating Effects of the Hydrazo Group References