"Life has evolved many molecular machines to perform mechanical tasks. Studying these machines promises insights into how machinery can generate force, how they assemble themselves, and how they evolved from simpler components. Ultimately this knowledge may inform synthetic biology projects to redesign existing, or evolve novel, machinery. Yet these insights have been hindered by our inability to visualize these machines as they occur in situ. The emergent technique of electron cryo-tomography, however, offers the ability to image this molecular machinery in situ, and will likely form the basis of much research on these machines due to its ability to resolve individual proteins within frozen living cells in three dimensions. Here I describe interdisciplinary work to dissect macromolecular machinery and understand its function and evolution using as 'testing ground' one of the most striking examples of molecular machinery, the bacterial flagellar motor. The flagellar motor is attached to a long filament that it spins to form a helical propellor, pushing the bacterium in favourable directions. Yet although the motor's many components and cellular role are known, the molecular mechanism of rotation and self-assembly remain enigmatic, and while its ancestry is established, how additional proteins are recruited to form novel machinery is poorly understood. Pseudo-atomic models of motors in situ will be generated using electron cryo-tomography together with development of tagging techniques to locate proteins. These structures will next be related to their mechanical output using single-molecule biophysical methods to understand the mechanical contributions of components. Finally, fundamental principles of the evolution of macromolecular machinery will be explored, both by studying recent elaborations upon motors in some bacteria, and by studying convergent evolution by the unrelated – yet analogous – archeaellum."