History of this Day started in 1992 from the UN Conference in Rio, where environmental problems were discussed and the huge value of environmental education of population of all countries worldwide in the context of realization of the sustainable development strategy was emphasized. The Day of Ecological Knowledge has been celebrated in Ukraine since 1996 at the initiative of environment NGOs. The main purpose of the Day is to inform the public about current situation in the field of environmental safety, compliance with applicable environmental laws. Conferences, seminars, round tables devoted to environmental problems are held during the Day. Building environment-friendly behavior based on environmentally friendly thinking is becoming more and more valuable for adequate reaction to changes and solution of environmental problems.