  Improved understanding of molecular systems has only emphasised the
sophistication of networks within the cell. Simultaneously, the advance of
nucleic acid nanotechnology, a platform within which reactions can be
exquisitely controlled, has made the development of artificial architectures
and devices possible. Vital to this progress has been a solid foundation in the
thermodynamics of molecular systems. In this pedagogical review and
perspective, I will discuss how thermodynamics determines both the overall
potential of molecular networks, and the minute details of design. I will then
argue that, in turn, the need to understand molecular systems is helping to
drive the development of theories of thermodynamics at the microscopic scale.
