Constructed wetlands (CWs) refer to artificially designed systems with the main function of wastewater treatment. For effective cleaning CWs imitate the self-cleaning ability of nature, which makes such systems simple. Moreover, CWs don't have a large construction impact and its system interference has the natural appearance. These systems are already relatively widespread and are getting popular across Europe. As the European area has very different geographical, geological and climatic specifications, the designing of the system should be adjusted according to the specific location. In my degree work I present the CWs in general, together with the practice in European countries, such as Denmark, Austria and Italy. Within my work I compared the guidelines, which are prescribed for the design of systems for each country, mentioned above, and existing systems in these three countries and Slovenia. I have identified the systems with horizontal and vertical flow of water, which are dimensioned for the treatment of wastewater. Based on the experience of Denmark, Austria and Italy, I derived the guidelines, that can be applied for the Slovenian territory. While analyzing the data, I have found differences between countries, which are caused by environmental factors and guidelines assumed in each country.