The article analyzes key theories, reasons for building and functioning of integrated entrepreneurial structures. The authors regard the essence of mergers and acquisitions (M & A) as economic phenomena dealing with capital concentration, which makes it possible to highlight their gradual complication with each stage of global economy development. They define the notion ‘integrated infrastructure of entrepreneurship’, which means a sum total of economic business units that reach mutual coordination in organizational-economic and financial-credit fields in order to resolve common problems and obtain synergy effect. The article studied two principle theories available in today’s economics substantiating benefits of company amalgamation through M & A into integrated business structures: the theory of synergy or the theory of added economic value growth and the theory of pride. By researching detailed classifications of reasons for M & A of companies, goals of integration agreements in view of their participants the classification of reasons was worked out by the following classification signs: reasons of current work efficiency, finance reasons and reasons for gaining competitive advantages. Specific features of home practice in the field of M & A operations were identified and characterized, which include bankruptcy and raiding.