Principles, Techniques, and Tools is a famous computer science textbook by Alfred V. Aho, Ravi Sethi, and Jeffrey D. Ullman about compiler construction. Although decades have passed since the publication of the first edition, it is widely regarded as the classic definitive compiler technology text.

It is known as the Dragon Book because its covers depict a knight and a dragon in battle. The first edition is informally called the "red dragon book" to distinguish it from the second edition and from Aho & Ullman's Principles of Compiler Design (1977, sometimes known as the "green dragon book" because the dragon on its cover is green).