The article is dedicated to theoretical aspects of forming a tax portfolio of a region. The main tool for achieving the effectiveness of the existing tax system is the tax portfolio. The article describes the structure and composition of the tax portfolio with the following characteristics: the level of the portfolio structure, types of taxes depending on the level of the budget elasticity, the quantitative characteristics of structure, qualitative characteristics of the structure by type and by total tax rates, qualitative characteristics of the arrears of tax revenues in the region, the quality of management of the tax portfolio. It is proposed to consider the types of tax portfolios by the degree of elasticity. The elasticity coefficient demonstrates the change in the share of the tax burden of the region when the gross regional product changes. The article also considers external and internal factors of tax portfolio formation in the region. The external factors include trends in the development of the national and world economy; the development of neighboring and closely related regions, the country as a whole; the economic and fiscal policy implemented at the federal level; the programs on special economic zones; the level of development, balance and reliability of the tax system. Regional internal factors are trends in the economic development of the region, including the number and structure of the population; directions of development of individual sectors of the economy and industry; the amount of working population officially paying taxes; the financial status of economic entities; the number of operating enterprises. One of the most important factors is the tax policy, whose main tasks for 2017–2019 are aimed at stimulating the activity of small and medium-sized businesses, ensuring the balance of regional budgets, stimulating the growth of trade turnover of Russian retail chains, reducing the federal budget deficit, improving tax administration and optimizing the existing tax benefits. The study of the tax portfolio of the region allows to manage the volume of tax revenues, change the structure of the portfolio, as well as optimize the tax portfolio in order to reduce the tax burden. Further research will focus on the analysis of tax portfolios of the regions and the management of tax portfolios of the regions based on the points discussed in the paper.