Customs is an institution responsible for tax collecting duties and taxes due to the entry of goods into the territory. As such, it has often been in the past, and sometimes still is, the main source of income for some states. Its activity is regulated by national law, but also by international agreements (WTO, free trade treaties, etc..).
It can also perform other tasks, including economic (fight against unfair practices, for example) and protection and security (anti-drug, control of hazardous goods, control of migration flows of people, sometimes Coast Guard, ...).
According to the country, it may be military status (such as the Italian Guardia di Finanza) or civilian. In France, it is represented by the Directorate General of Customs and Excise (DGDDI).
The customs regime is the framework within which one chooses to return the goods vis-à-vis the customs authorities. The selection is made by filing a customs declaration.
Why are many customs procedures?
Having multiple customs regimes can best reconcile the sometimes conflicting interests
* Customs authorities primarily interested in collecting taxes and duties, and enforce regulations
* Companies that want to carry goods as freely, quickly and economically as possible
A customs procedure typically corresponds to a "scenario" of international trade (transport of goods by road quickly, for example, for the TIR), arranged to meet customs regulations. A commodity can move from one plan to another as needed.