Efficiency of the capital concentration processes can be measured using a variety of tools. Various studies often refer to market data and to valuation of companies' equity before and after takeover transactions. Such studies provide valuable information, but they concern only a small group of companies - those listed on regulated capital markets. The research carried out by the author is an important addition to previous scientific publications. The author used a unique database of merging companies in Poland. The database includes companies that had been entered into the National Court Register, regardless of whether they were a member of a regulated capital market. There have been many studies in the field of finance and management that covered the moment of making the decision to merge and the next step - concentration of capital. Researchers focus on the moment of announcing the intention to merge companies and the years following the merger. There are few publications that examine companies in the periods preceding a merger. Based on literature review, it can be concluded that there is no Polish publication examining Polish companies in the periods preceding a merger of business entities. By focusing on the preparation of companies for a merger, that is, on the period right before the merger, this monograph fills in this gap. The main objective of the article was to analyse the phenomenon of shaping the profitability of Polish acquiring companies in the period preceding the registration of the merger. The main goal was achieved by developing specific goals in particular chapters of the publication. Research methods used in chapter 1 were based on the analysis of the phenomenon of capital concentration in both Polish and international environment. To this end, capital concentration processes were analysed from, inter alia, a sectoral, a formal and legal and a cross-border perspective. The analysis of the first chapter's data was used - by deduction - to indicate the weight and multidimensionality of the research problem raised in the publication. The second chapter attempts to identify the most important - from the perspective of analysing the economic activity of companies - parameters for the assessment of their effectiveness. In this chapter, the fundamental research methods were analysed and, based on it, deduction concerning determinants of capital concentration was made. Empirical verification of research hypotheses is included in chapter 3. All research hypotheses were verified using statistical research methods: correlation analysis and regression analysis. On this basis, using deduction methods, it was possible to draw conclusions regarding the shaping of the operating profitability of assets in Polish acquiring companies in the periods preceding the merger of business entities. The first research hypothesis (H1) assumed that there are selected parameters of business entities that have a significant impact on the results achieved by acquiring companies, measured by the operating profitability of assets. After presenting in chapter 2 the parameters of companies deemed important for the purposes of the study, this hypothesis was subject to empirical verification in chapter 3. The first hypothesis was positively verified. Based on correlation and regression analyses, in the periods preceding the merger of economic entities it was noticed that not all the determinants of the shaping of operating profitability recognised on the basis of the author's findings and literature review were statistically significant in companies belonging to various sectors of economic activity in the years preceding the merger. However, it was noted that the impact of the financing structure (the share of liabilities in total capitals) and the structure of assets (the share of fixed assets in total assets) had a negative impact on the shape of the operating profitability of assets. Verification of the first hypothesis allows us to conclude that the author's contribution to understanding the theory and practice of mergers consists in indicating the determinants of positive and negative dependence on the operational profitability of assets. The second research hypothesis (H2) indicated that there may be anomalies in the shaping of those company parameters that are responsible for the companies' effectiveness, measured by the profitability of assets, in the periods preceding the merger. The study of the relationships between parameters covered the years preceding the merger. Introduction to empirical verification of the second hypothesis (discussed in chapter 3) is to be found in chapter 1 and it consists in a presentation of the motives behind capital concentration as well as the various forms of merging companies and a sectoral approach to merging companies. The second hypothesis has been positively verified. Pointing to the results of verification of the second hypothesis, it can be concluded that statistical significance of determinants has been investigated. Significant and irrelevant determinants have been specified, and - through empirical studies - non-linear dependencies between some determinants have been proved, which until now has not been done in literature. The third hypothesis (H3) developed the second one (H2), and its objective was to check whether a financial crisis happening in the studied period has any impact on the shaping of the operating profitability of assets of companies merging business units. Verification of the third hypothesis started with an investigation included in chapter 1, which - based on the financial data of companies commencing capital concentration, given in calendar years - aimed to verify whether the years of the financial crisis had a significant impact on the number of transactions or on the manner of running the merger process. On the basis of the conducted study, the third hypothesis was not verified positively. The result of the verification of the third hypothesis is an interesting one, for it indicates that the financial crisis has to impact on companies' preparation for a merger. This is a very important conclusion, given that the author states that empirical research requires the manipulative preparation of the financial condition of the acquiring company to be discontinued. In the monograph, through the analysis of the correlations between variables, it was noted many times that the dependencies are not rectilinear. Numerous publications in the field of finance and management assume that the correlations are linear (the Pearson correlation is used then). Based on the conducted research, it is concluded that there are strongly correlated variables, whose dependencies are polynomial. This means that, theoretically, there are local extremes, minima or maxima, depending on the marks of the directional coefficients. This conclusion indicates that the relationships cannot be simplified for the purposes of studies, and behaviour in business practice is often not linear. The results of the study develop the field of finance in terms of merger and capital concentration, as the author proves the existence of different relationships than those previously described in the literature.(original abstract)