A Chapter is a two-digit grouping in the Harmonized Tariff Schedule that organizes goods by broad category. There are 99 chapters in the international Harmonized System, though Chapter 77 is reserved for future use and Chapters 98 and 99 are reserved for national use (in the U.S., Chapter 98 handles special classification provisions and Chapter 99 handles temporary tariff modifications like Section 301 duties).
Chapters are grouped into 21 Sections, each representing a major class of trade — for example, Section XVI covers machinery and electrical equipment (Chapters 84–85), and Section XI covers textiles (Chapters 50–63).
Each chapter has Chapter Notes that are legally binding for classification purposes. These notes define terms used in the chapter, exclude certain goods, and provide essential interpretive guidance. Never classify a product without reading the applicable section and chapter notes — they often contain the answer.