We combined targeted chemistry and computational design to create a crystal structure for porous chromium terephthalate, MIL-101, withverylargeporesizes and surface area. Its zeotype cubic structure has a giant cell volume (∼702,000 cubic angstroms), a hierarchy of extra-large pore sizes (∼30 to 34 angstroms), and a Langmuir surface area for N ₂ of ∼5900 ± 300 square meters per gram. Beside the usual properties of porous compounds, this solid has potential as a nanomold for monodisperse nanomaterials, as illustrated here by the incorporation of Keggin polyanions within the cages.