Tax inspection supervision is implemented by Financial inspectors of the Financial Administration of the Republic of Slovenia. Their activities in the field of value-added tax are primarily aimed at detecting and preventing frauds of this tax. The diploma thesis presents tax inspection supervision and the issue of systemic value-added tax evasion - carousel fraud. The emphasis is on reviewing the effectiveness of the work of financial inspectors and on their coping with tax carousels. In the theoretical part, a descriptive method and a secondary analysis were used, for description of the basic characteristics of tax control and to analyse the tax inspection supervision and the problem of carousel fraud. In the empirical part, the work of financial inspectors in the years 2017-2019 was analysed using the data analysis method. Data were obtained from the annual reports of the Financial Administration of the Republic of Slovenia but also some data is acquired from the reports of the Inspection Council. For the survey, a questionnaire was sent to the General Finance Office. The results of the analysis showed that financial inspectors are successful in their work in the field of value-added tax. This is seen as an increase of inspections in the field of the value-added tax year by year and an increase in the collection of funds from value-added tax while implementing a series of preventive and remedial measures in the fight against carousel frauds. The research also found that the Tax Procedure Act unequivocally and sufficiently defines the tax inspection procedure, while the Financial Administration Act determines the appropriate powers of financial inspectors to act effectively in the tax inspection supervision. The results of the analysis of the operation of financial inspectors (with an emphasis on value-added tax) provide an insight into their work in 2017-2019.