have fabricated the first materials with a tunable pore structure at the atomic level and a narrow pore-size distribution [Nature Materials (2003), 2, 591]. The interaction of porous solids with gases and liquids is essential for many applications from molecular sieves to gas storage, catalysts, adsorbents, electrodes, supercapacitors, filters, and biomedical devices. Large pores can be produced in many materials, but sizes of 2 nm and below can only be fabricated in carbons or zeolites. Zeolites have a narrow poresize distribution, but discrete pore sizes or fine-tuning is impossible. Porous carbons, on the other hand, which are produced by thermal decomposition of organic materials, can have pore sizes down to 0.3 nm, but usually have a broad pore-size distribution. Using carbide-derived carbon (CDC), the researchers achieve unprecedented control of the size, shape, and uniformity of the pores. The material is produced by extracting metals from carbides using chlorination. The metal carbide lattice serves as a template, while the layer-by-layer metal extraction allows atomic-level control of the structure. By varying the chlorination temperature the researchers were able to produce a CDC from Ti 3 SiC 2 with a pore-size distribution comparable to that of zeolites. At low temperatures, pore sizes as small as 0.3354 nm were achieved, which is only slightly larger than the interplanar spacing in graphite. CDCs produced above 700Β°C have mesopores, the volume and size of which increase with increasing temperature. The pore size can be controlled with an accuracy >0.05 nm.