Numerous nonviral systems have been developed for the delivery of nucleic acids to cultured cells and to particular cell types in vivo. These systems vary with regard to their toxicity, immunogenicity, and ability to target particular cell surface receptors and/or cell types. A class of linear cationic polymers containing the sugar β-cyclodextrin has been shown to be effective at delivering a variety of nucleic acids in vivo, including plasmid DNA, DNAzymes, and short interfering RNAs (siRNAs). These polymer-nucleic acid complexes (polyplexes) can be further modified to incorporate a targeting ligand such as transferrin to induce preferential uptake of polyplexes by cells expressing high levels of the cognate receptor. This article presents background information on cyclodextrin-containing polycations.