In recent decades, the need to protect the natural environment became a repetitive focus of attention of public opinion worldwide. Consumers are increasingly realizing the importance of protecting the environment through product choice while companies are increasingly considering the impact of their activities to the environment. At the same time, the global economic crisis resulted in increased national and international competition, stimulating the use of green marketing practices as a source of strategic competitive advantage, and contributing to an increase in national competitiveness of countries that employed these practices.  The paper begins with a summary of scholarly literature in the field of green marketing, then offers clarifications on the concepts of organizational and national competitiveness, and defines a set of indicators to assess the results of applying green marketing principles and practices at a national economy level. On this basis, the authors propose an original methodology for calculating the Index of Green Marketing at a country level.  Later, based on the assumption that the degree of implementation of green marketing principles and practices positively influences competitiveness, the authors correlated the Green Marketing Index values calculated for European Union countries with the Global Competitiveness Index values calculated by the World Economic Forum for these countries.