Abstract: A foldable portable building can be collapsed to fit within the outside dimensions of an internationally standardized (ISO) goods container to facilitate mechanical handling and transportation. The building comprises a rigid main support having a main floor section, a main wall section and a main roof section. When the building is extended, generally horizontal and planar, hingedly interconnected floor sections and roof sections extend from the main floor and roof sections respectively, and wall sections extend between the said sections. The wall sections comprise an end wall section, two first wall sections and two second wall sections which are hingedly interconnected similarly to a bellows. When the building is collapsed, the wall sections are located adjacent the main wall section, the roof sections are disposed vertically on a side of the wall sections remote from the main wall section, and the floor sections are disposed vertically outwardly of the folded wall and roof sections.