The significance of American expos in the history of world’s fairs, as well as in the history of planning, urban design, architecture and landscape architecture is extraordinary. In the article, which constitutes the first part of a report on the carrying out of the research project entitled “Urban and architectural heritage, as well as the impact of American world expos on city planning and development”, a retrospective outlook on American world expos has been presented on the examples of New York and Chicago, with a particular focus on their long-term heritage, which affects the development of their host cities.