Transposons are small pieces of DNA that can transpose through either RNA or DNA intermediates. They have been found in almost all organisms and are important components of the evolutionary process at the chromosomal level. They have provided the raw genetic material that has produced domesticated genes that now provide important cellular functions and are now being explored as genetic tools in both humans and insects that vector human pathogens. Here I compare the requirements for both insect and human gene therapy and discuss the similarities between them in terms of transposon performance. Recent progress in understanding transposon function in terms of transposase structure is described as is the rapidly emerging role of RNAi in generic transposon regulation. These developments reinforce the view that, autonomous, transposon behavior in host organisms is, in part, determined by the nuclear and cellular environment of the cell and these factors need to be considered when developing transposons as therapeutic agents either in humans or in insects that vector human disease.