The chemistry, scope, and limitations of the azide method of peptide synthesis are discussed with special emphasis on side reactions encountered during the preparation of hydrazides, azides, and in the coupling process. Curtius rearrangement, racemization, and amide formation are part of the discussion. 1. The Formation of Hydrazides 2. Side Reactions in the Preparation of Hydrazides 3. The Preparation of Azides from Hydrazides 4. Side Reactions during Azide Formation 5. Acylation with Azides 6. Side Reactions in Azide Coupling 7. Modifications of the Azide Method 7.1. The Honzl-Rudinger Method 7.2. The Medzihradszky Method 8. Racemization in Coupling with Azides 9. The Azide Method in Solid-Phase Peptide Synthesis 9.1. The Preparation of Peptide Hydrazides 9.2. The Building of Peptide Chains 10. Cyclization with the Azide Method 11. Polymerization by the Azide Method 12. Acyldiimides