  DNA nanotechnology promises to provide controllable self-assembly on the
nanoscale, allowing for the design of static structures, dynamic machines and
computational architectures. In this article I review the state-of-the art of
DNA nanotechnology, highlighting the need for a more detailed understanding of
the key processes, both in terms of theoretical modelling and experimental
characterisation. I then consider coarse-grained models of DNA, mesoscale
descriptions that have the potential to provide great insight into the
operation of DNA nanotechnology if they are well designed. In particular, I
discuss a number of nanotechnological systems that have been studied with
oxDNA, a recently developed coarse-grained model, highlighting the subtle
interplay of kinetic, thermodynamic and mechanical factors that can determine
behaviour. Finally, new results highlighting the importance of mechanical
tension in the operation of a two-footed walker are presented, demonstrating
that recovery from an unintended `overstepped' configuration can be accelerated
by three to four orders of magnitude by application of a moderate tension to
the walker's track. More generally, the walker illustrates the possibility of
biasing strand-displacement processes to affect the overall rate.
