Residential architecture in Otwock is a reflection of the historical phases in the spatial development of the city, shaped, with certain exceptions, from the end of the 19th century. The individual districts of this locality have varied urban planning and architectural character. The identified Modern interwar buildings are present within the limits of several of these. They are integrated with the natural landscape: a forest complex and the Świder River valley. Primarily, they are found in Śródmieście [Downtown], Świder, Soplicowo, and Śródborów. Modern single– and multi–family buildings supplement the urban tissue in the present city center. They mainly represent early and moderate Modernism. Similarly, there are not many examples of Modernism in Świder. The greatest number of buildings with the qualities of Modernism understood as symbols of modernity and progress that were built and have survived to this day are the pride of two formerly peripheral housing estates: Soplicowo and Śródborów. Building tissue here was shaped differently than in historical areas, developed in different parts of the city as early as the end of the 19th century. They differed in their genesis and method of land parceling. Construction on the grounds of Soplicowo was initiated by Edward Kasperowicz, together with other partners, in a residential colony for civil servants. Śródborów was created thanks to the initiative of the “Śródborów Society.” The development of these housing estates was obviously the result of the new way of thinking in urban planning (the then popular concept of the garden–city) and their founding as new housing projects on virgin land. The structures located here are distributed amidst vegetation with composed forest gardens and small–scale architecture that, in many cases, has maintained its initial dimensions and architectural solutions. These are successively subject to changes, modernization, or even demolition. Nevertheless, these areas continue to be the site of interesting and little known examples of the architectural activities of recognized Warsaw architects as well as local builders, undertaken for investors of varied social standing. The presentation of these examples – buildings from the years 1918–1939 – is the objective of this article. It is based on many years of own research, including materials collected and developed within the framework of a fellowship from the Ministry of Culture and National Heritage from the 2nd half of 2018. The article also contains new, previously unknown information as well as discovered, unpublished archival designs from the collections of various archives. It also takes advantage of existing topical literature. The article discusses Modern buildings against a backdrop of the history and spatial development of the city of Otwock. The conducted analyses demonstrated the characteristic features of their architecture and pointed out the need to preserve and protect the most valuable examples for future generations. This article was in part made possible with the kind support of Professor Małgorzata Rozbicka, who I want to thank at this point.