The purpose of the article is a synthesis of methodological tools for monitoring and assessing the level of monopolization in the economy. The following methods have been used in the article: modeling, graphics, index. Result of the paper is a synthesis of methodological tools for monitoring and assessing the level of monopolization in the economy. Among these methods the features of the model of compromise by O. Williamson, Herfindahl-Hirschman Index (ESI) and the concentration index (CR) have been disclosed in more details. Model of compromise of O. Williamson allows determining the effects of concentration of production. Its advantage is the possibility to assess the overall social effect of the individual processes of concentration of production based on cost comparisons of costs reduction by increasing production scale and increase in net losses from a possible price increase of sales. ESI index is used in the analysis of competition and takes into account the market share of each participant. In turn, the CR Index is an indicator that reflects the market share (or index concentration) of a selected number of large-volume players or the amount of their shares on the market. Scientific innovation is to use a systematic approach to the methods of monitoring, covering model, graphic, index methods along with analytical. The practical significance of the paper is a synthesis of methodological tools of assessment the level of monopolization in the economy and the possibility of using a graphical method for evaluating the results of business operations of mergers, acquisitions and associations of enterprises. Prospects for further research are to deepen methodological tools of monitoring, combination of different methods to solve specific industry and scientific tasks, justification of model bases of monitoring the state monopolization of various industries.