Sustainability and sustainable development have become important concepts and goals across science and society. Sustainability, connected to desirable long-term conditions, is an inherently applied in public sector, public procurements. Every year the European Union (EU) Member States collectively spend around 14% of Gross Domestic Product (GDP) on public procurement. In Latvia, public procurement accounts for 17% of GDP. The review of the new public procurement directives and their transposition process in Latvia plans to show new opportunities for green public procurement (GPP) application: the contracting authority will be able to reject, for example, an abnormally low bid, include environmental management system requirements in the selection criteria, use life cycle costing criteria, etc. GPP is the systematic integration of environmental criteria into all activities related to the procurement of goods or services, from the identification of needs, the development of appropriate specifications and evaluation procedures, to the monitoring of the results achieved. The aim of the work is to analyse sustainability theory and explore the application of GPP to improve the quality of GPP through sustainability. With a view to increasing sustainable consumption over the last 25 years, several initiatives have been developed. The United Nations World Commission on Environment and Development developed the Concept of Sustainable Development "Our Common Future (1987)", that was widely used in the context of the United Nations Conference on Environment and Development held in Rio de Janeiro in 1992. Sustainable development concept was defined at the international event in 1995 in Oslo "use of goods and services that respond to basic needs and bring a better quality of life, while minimizing the use of natural resources, toxic materials and emissions of waste and pollutants over the life cycle, so as not to jeopardize the needs of future generations" (Giulio, Fischer, et al., 2014). The Organization for Economic Co-operation and Development (OECD) made "green growth" its 2011 slogan (Lorek, Spangenberg, 2014). The green economy became a pillar of major European and international strategies: most notably in the Europe 2020 strategy adopted in 2010 by the EU to drive sustainable growth, and in the Rio+20 outcome. The incentive to use GPP is based on the fact that in many countries public sector spending amounts to a significant part of the economy, and that this purchasing power can be used to influence production and consumption to achieve desired reductions on environmental impact (Lundberg, S., Marklund, P.O., Strömbäck, E., Sundstrom, D., 2015). When public authorities go green, they make an invaluable contribution to environmental protection and sustainable development, setting a trend that often convinces other to follow suit (Day, 2005). The practice amounts to significant expenditure, excluding utilities and defence, across Europe, comprising 13% of European GDP in 2015 (Commission, 2016). In the last decade, the use of environmental criteria in public tenders has been increasing defusing (Testa, F., Iraldo, F., Frey, M., Daddi, T., 2016). The implementation of GPP is covering new sector in recent years, identifying new practices (Cheng, W., Apolloni, A., D'Amato, A., Zhu, Q., 2018). The challenges that the European municipalities face on a path towards sustainability were outlined, along with the undertaking of sustainable procurement and the active promoton of sustainable production and consumption, particularly, eco- labelled, organic, ethical and fair-trade products (Belgica, P.B., Jose, B.C.M., 2016).

Keywords: sustainability, green procurement, sustainable theory