We synthesized a new class of organic nanoporous polymers using cyclodextrins as basic building blocks. These processible nanoporous polymers were named 'nanosponges' because they have nanometer-size pores (distribution 0.7–1.2 nm) and exhibit superior ability to absorb organic molecules in water. Cyclodextrin cavities provide a hydrophobic environment and hence generate a strong affinity to organic molecules at water-solid interfaces. Indeed, the formation constant (K) of polymeric cyclodextrins and organic guest molecules is more than eight orders of magnitude larger than molecular cyclodextrin systems in water, and yet the process is completely reversible in organic solvents such as ethanol. The significant potential of these results is that hazardous organic contaminants may be reduced to parts-per-trillion levels in water by these polymers, as measured by ion-trap mass spectroscopy and UV-visible spectroscopy.