Conception of Cartels: Definition and Diversity.- Cartel Occurrence and Operation in Market.- Cartel Markets.- Legal Regulation of Cartels.- Analysis of the Impact of Cartels on National Economy and Competitiveness.- Critical Analysis of Economic Efficiency of Fines Imposed on Cartels.- Methodological Principles of Assessing Cartel Harm (Effects).- Assessment of Cartel Impact on the National Economy: Integrated Model.- Empirical Application of a Model for an Integrated Assessment of Cartel Impact on the National Economy in the Case of Lithuania.- Recommendations to Minimise an Adverse Impact of Cartels on the National Economy.- Conclusions.- Annexes.