There are two major systems used to classify imports and exports.
The Standard International Trade Classification (SITC) was developed
by the UN and has been in use since 1950.
The code can be
browsed online at the UN
The Harmonized System or Harmonized Tariff System was created in 1988
and has been revised more frequently. It is maintained by the World
Customs Organization. This code is not freely available.
The US maintains its own codes, which are based on the Harmonized
System. These have greater detail than the Harmonized system.