Customs and customs administration are very important areas for the circulation and trade of goods, services and information. Everything entering or leaving a certain country must be written down and informations must be available. The Customs Administration is precisely the competent authority that provides insight into customs affairs in the Republic of Croatia. It is important to be able to explain the way the Customs Administration works, the handling of customs declarations, the way it operates, and to study the audit of the company compiled by the competent authorities, in order to understand its importance in the trade itself and the state in general. For the crossing of goods across the border, the customs declaration is important, which starts the recording of traded goods, and with the audit of the Customs Administration itself, which is carried out by the competent authorities, we can determine the circulation of all goods and data. We can determine its business and see all information about the business. By analyzing the operations, all the advantages and disadvantages of the operations of the Customs Administration can be observed, provide information on operations over a period of time and, most importantly, how to improve the operations themselves.