Studies of several transposable genetic elements have pinpointed the importance of the transpososome, a nucleoprotein complex involving the transposon ends and a transposon-encoded enzyme--the transposase--as a key in regulating transposition. Transpososomes provide a precise architecture within which the chemical reactions involved in transposon displacement occur. Data are accumulating that suggest they are dynamic and undergo staged conformational changes to accommodate different steps in the transposition pathway. This has been underpinned by recent results obtained particularly with Tn5, Tn10 and bacteriophage Mu.