An improved modular building panel and system for building construction is disclosed. The improved modular building panel comprises a novel honeycomb or lattice core comprising multiple layers of corrugated, preferably metal, components mechanically connected by any means known in the art, but which may be chemical bonding. External cladding layers comprising a novel cement mix comprising, in a preferred embodiment, Portland cement, silica sand, perlite, glass beads, and water, in combination with the honeycomb structure, provide a lightweight, highly durable, low-cost, projectile resistant, highly insulating, water, mold and mildew resistant, wind resistant novel modular wall system which is adapted for use in commercial, residential, and other construction and which provides superior security to the user. The modular building panel and system of the invention may be utilized for walls, roofs, floors, bridges, or other structures.