The main purpose of the article was to assess the eco-socio-economic development of world countries. For this purpose, the Comprehensive Eco-Socio-Economic Development Index (CESEDI) was proposed and used. The proposed measure is based on a dozen or so indicators recognized and used in the literature for assessing countries in terms of their social, economic and environmental achievements. An attempt was made to include most of the elements necessary for the safe, healthy and happy life of citizens of the studied countries. The article presents world leaders, based on the CESEDI. Moreover, the individual components of the CESEDI and their level in the analyzed countries are presented. It was found, inter alia, that 18 out of 20 countries with the highest CESEDI are European countries. The ranking leaders were highly developed Scandinavian countries (Norway, Denmark, Finland) and Switzerland. The countries of Eastern and South-Eastern Europe (Slovenia, Slovakia, the Czech Republic, Poland and Romania) took high positions in the ranking, ahead of such countries as Canada, the United Kingdom, Japan and the United States. Research results indicate that European and South American countries are, on average, more developed in terms of ecological, social and economic development than countries in the rest of the world.