Understanding how and why a machine works in the way it does is crucial for optimizing designs and inventing new ones. For macroscopic machines such an understanding can be deduced from engineering principles and Newtonian physics. In contrast, at the molecular level there is no simple explanation for why individual components of biomachines move in a particular way. Is the movement of a specific amino acid in ATP synthase a key requisite for the mechanism, or does it occur incidentally as part of an evolutionary pathway that was overall successful? Biomolecular machines operate autonomously, apparently through Brownian ratchet mechanisms. They use energy and information to rectify the directionality of random thermal movements of their components so that work can be performed. This type of machine includes biological pumps and motors, in which the energy is generally provided in the form of a chemical potential gradient. Chemists are learning how to design synthetic analogues of such machines, with examples including a minimalist autonomous chemically-fueled molecular rotary motor (Fig. ).