Gene therapy is one of the most important developments for modern medicine. As such methods for the compaction and delivery of nucleic acids bearing therapeutic sequences is essential. The quest for non-viral carriers of nucleic acids has produced a number of possible candidates with dendrimer being among the most promising. Their hyper-branched structure and well-defined size together with low cytotoxicity has found success in both ex-vivo and in-vivo studies. The compaction of DNA with dendrimer has produced a rich array of different structures depending on the physiochemical conditions. Mechanisms that drive the compaction have been shown to be a number of physical interactions that reduce the large polymeric entity from 100s of nanometers to some tens of nanometers to fit into the cell nucleus. The mechanisms driving the compaction of DNA will be discussed in detail while the focus will be directed to tuning the structural properties of the complexes and their structural characterization using small-angle scattering techniques.