This paper aims to understand the spatial characteristics of pilotis in modern architecture. Looking back to the past, there was neither physical nor mental restriction as to when and where to communicate. We can say that in the modern days, however, people are literally drawing boundaries to clearly distinguish the function or property of a certain space from another, leaving less and less ambiguously defined spaces. People are left with no opportunity to be in contact with the environment.<br> The society today is forced to make efficient use of the limited resources they possess to live a full and sustainable life, requiring buildings and cities to create spaces that are open to the surroundings, allowing states of ambiguity without any apparent boundaries. It can therefore be said that the society is in demand for what we in this paper call “boundary spaces”; a “boundary space” is a boundary “line” with a volumetric or spatial thickness which not only defines the perimeter of a space, but also functions as a bridge to connect the worlds on both sides. There is no obligation as to who steps in to this boundary space, which would eventually trigger diversity in the activities within the space and its surroundings.<br> Even though the application of piloti spaces has been a method frequently used in the architecture field as a strategy to create boundary spaces, it has never been evaluated as a device to create open spaces to house diverse activities. Based on such background, we set the main goal of this research to introduce a new conceptual framework of pilotis, in which piloti spaces are defined as boundary spaces to trigger unintended and uncontrolled activities that mediate all the possible architectural connections there is; the inside-outside, the private-public, the artificial-natural, and the architecture-city relationships.<br> We begin this paper with a case study of pilotis in the modernist period, focusing mainly on the components and the layouts of piloti spaces that function as boundary spaces. The overall time span of the analysis is 55 years, starting from 1926 when Le Corbusier systemized pilotis as one of the elements of “Les 5 points d`une architecture nouvelle,” up to 1980 when post-modernist architecture became a trend.<br> The 126 cases referred in this research were taken from 6 representative architecture magazines in Japan; “Shin-Kenchiku,” “Kenchiku Bunka,” “a+u,” “Kokusai Kenchiku,” “Kindai Kenchiku,” and “SD.” The essential dimensions of the piloti spaces could be measured with detail in every case.<br> At one stage of the research we extracted the measurements of ceiling heights, the sections of the ceilings and the floors, and the furniture pieces placed within the space, all of which relate deeply to what is happening in the piloti spaces. By both examining these physical elements and referring to the way the piloti spaces are connected to the environment, we came to a general understanding of the characteristic trend that piloti spaces possess. We also considered the architects' intentions of integrating pilotis in the building design.<br> The 126 cases were classified according to how the piloti spaces can be approached from the outside, along with how the piloti spaces are in relation to the interior spaces. Through the process we came to experimentally conclude that pilotis possess one or many of the following roles or characteristics: (1) a gate-like space to welcome people in from the outside, (2) an isolated backyard, (3) a front yard that allow diversity in movement, (4) division between the inside and the outside, (5) a correspondence to the topographical conditions, (6) a separation from the ground.