The article elucidates main scientific approaches to understanding of essence of management accounting. From scientific studies of domestic scientists it is concluded that most of them classify management accounting under competence of accounting in general. It is shown that the first institutional factors concomitant with division of general theory of accounting into financial and management components were development of forms of business and implementation of accounting standards and manuals. Additional institutional factors leading to present-day frequent interpretation of management accounting as ?shadow book-keeping? are economic and fiscal opportunism of businessmen and managers. The statement is grounded that the management accounting as integral component of accounting in general is embodiment of the best accounting practice not regulated by accounting standards and manuals. It is demonstrated that the data of official financial accounting are used in managing of the companies. It is due to the fact that most of the financial accounting rules were set up by institutionalization of the key non-formal accounting rules. On the basis of this conclusion the necessity is proved for transformation of financial and management accounting into unified system of accounting which would be primarily directed towards management purposes but would provide at the same time, in accordance with the frame rules of accounting standards, financial reporting for needs of external users.