HSN stands for Harmonized System of Nomenclature. HSN was developed by the World Customs Organization (WCO) to classify the goods across the world in a systematic manner for the purpose of taxation in identifying each product. HSN classification covers more than 5,000 products, and it came into force from 1988. HSN is widespread and has been adopted by more than 200 countries for uniform classification, the base for customs tariff and for collecting international trade statistics.

Each product is assigned an HSN code. An HSN code comprises of six digits arranged in a logical structure. HSN classification was already in existence in India during the Central Excise and Customs regime, however, it became detailed in the GST with two more digits added to it. Hence, an HSN code in the GST regime contains 8 digits.

The HSN structure consists of 21 Sections with 99 Chapters, 1,244 headings and 5,224 subheadings. Each section is divided into a Chapter and each Chapter is divided into a Heading. Each Heading is further divided into a Subheading. Section and Chapter denote the categories of products or goods while Heading and Subheading denote the products in detail.
It is mandatory for a product to have all eight digits in case of export and import under the GST regime.