Nowadays, there is a greater need to innovate and implement sustainable technologies that contribute to the betterment of the world and move towards meeting the global goals of sustainable development. Sustainable technologies are an increasingly common topic in the modern world, and in order to raise the awareness of citizens and the countries in which they live, there is an increasing effort to influence innovations that consequently have a positive impact on the world and its sustainability. The aim of this paper is to present the current level of implementation of sustainable technologies in the Republic of Croatia and showcase a way of improving and better functioning of cities in the field of environmental protection and energy use. Apart from presenting the current level of sustainability of Croatia itself, the sustainable development and sustainable technologies of Denmark will be presented and they will serve as a model for a potentially more developed Croatia. Also, the goal is to analyze the attitudes of Croatian citizens in the area of satisfaction with the functioning of the Republic of Croatia as an aware state that takes the necessary actions to meet the goals of sustainable development. Croatia is currently a country that is aware of global challenges and is taking measures to facilitate the impact on the environment it creates. The world is becoming more educated by the day in the field of sustainable development and its needs, and Croatia's intent is to follow global trends and join the common goal of preserving the environment and responsible use of resources for present and future generations. The paper discusses the application of the principles of sustainable development in cities and countries, with special emphasis on renewable energy sources, digitalization and innovation in the field of sustainable technologies in the 21st century. In the paper, methods of comparative analysis, methods of description and methods of synthesis are used throughout, and conclusions are made specifically in the field of implementation of sustainable technologies and the very level of development of countries in the field of sustainability. The results of the paper indicate the existence of opportunities within Croatia as a potentially more developed country. It also highlights the potential for progress in the sustainable development sector at all levels; environmental, economic, social and similar, specified for the area of implementation of sustainable technologies with the aim of improving the existing content and reducing the negative impact on the environment and the system.