Abstract: A building module collapsible for transport and expandable for use, includes an elongated core section which has substantially vertical, lateral and longitudinal walls and a core floor section which together define a partially enclosed interior area. A floor assembly is connected to the core floor section for movement between folded and unfolded positions. Telescopic, as well as foldable wall, ceiling, floor and roof sections are provided and allow the building module when in its collapsed for transport condition to comply with the current United States Department of Transportation regulations pertaining to the maximum shipping sizes for standard ground transportation, as well as the current International Standards Organization codes pertaining to maximum shipping sizes for standard ground and water transportation.