All countries face several issues while running the process of sustainable development—the absence of a uniform means of sourcing investment for sustainable development and the lack of a unified index for the evaluation of sustainable development. No doubt, ensuring sustainable development requires constant financial investments. Hence, it is essential to examine the investment sources for sustainable development at the country level and to comprehend if the current financial investment has a direct impact on the results of a country’s sustainable development. The article aims at identifying the financing sources for sustainable development for each of the European Union (EU) countries and assessing their impact on each of the EU countries’ sustainable development, which is expressed as the Integrated Sustainable Development Index (ISDI). After the detailed analysis of investment sources for the sustainability of the EU countries, two sources of investment, assignation of budget and the EU structural funds, were selected, and ISDI calculation was applied for twenty-five of the EU member states for the period 2003–2017. Correlation analysis (using SPSS software) helped to identify the strength of the connection and to select countries for the Johansen Cointegration Test (using Eviews software) in order to determine how variables interact. The results show that the combination of the assignation of budget and the EU structural funds has a positive impact on the coherence of five (Czech Republic, Denmark, Spain, Slovenia, and Austria) out of twenty-four countries.

Purpose – is to analyse the different investment sources for sustainable development of a country and reveal the interaction between investment sources for sustainability and a country's sustainable development. Research methodology – analysis of scientific sources, collection and systematization of statistical data, a method for sustainable development index calculation, correlation regression analysis. Findings – each analysed country's progress of sustainable development is expressed as integrated sustainable development index revealed that all analysed countries are gradually increasing their sustainable development results. All three analysed investment sources are strongly affecting countries sustainable development, and stochastic relationship exists between variables. Research limitations – statistical data with incomplete time series, for which not all the most important sustainable development indicators were selected. The case of three Baltic countries (Lithuania, Latvia, and Estonia) is used for the period 2003–2017. The three main investment sources for sustainable development of a country: assignations of the state budget, EU structural funds, and direct investments, are chosen for the research. Practical implications – results can be used in calculations for other countries sustainable development and investments interactions. They can be used to evaluate the impact of the different source and contribute to the modelling of their use. Originality/Value – this article is unique because it reveals the interaction of multiple sustainability sources, in terms of investment sources for sustainability and the results of a country's sustainable development. These sources can be supplemented and adapted to other countries (at least in developed countries EU level). Keywords: sustainability, sustainable development indicators, integrated sustainable development index, assignation of the budget, EU funds, direct investment