Nonviral delivery systems, while generally less effi cient than viral vectors in transfecting the lung epithelium, are increasingly used to deliver smaller DNA/RNA molecules (Table 1 ). Strategies include the use of DNA-lipid and DNA-polymer complexes and naked DNA/RNA oligonucleotides, such as siRNA [28] , decoy oligo nucleo tides [29] and plasmid DNA [30] . Nonviral delivery systems are less immunogenic than viral vector-based approaches, and can be generated in large amounts at relatively low cost.