This invention relates to prefabricated, lightweight, multi-component structural modular building panels and modular building systems. The said panels are framed with edge members that have a unique connecting shape, making them modular. The multi-component panel allows for design flexibility and the mass manufacturing of its components. Connectors serve as a link to assemble the panels together, and to connect them to corners, floors or foundations, roof panels and the roof apex member, and or other conventional construction elements. Connectors and members, all with unique connecting shapes, coupled with the said panels, create a structural wall, roof, similar structure or building system. Assembled panels and members incorporate the primary building structure and the building envelope. The assembled panels, members and other components of the building system, in part or whole, can be flat packed for easy transport and shipping, and can be assembled quickly and easily with semi-skilled labor.