We measure fundamental properties of single molecule devices, seeking to understand the interplay of physics, chemistry and engineering at the nanometer scale. The underlying focus of our research is to fabricate single molecule circuits, a molecule attached to two electrodes, with varied functionality, where the circuit structure is defined with atomic precision. We measure how electronic conduction and single bond breaking forces in these devices relate not only to the molecular structure, but also to the metal contacts and linking bonds. Our experiments provide a deeper understanding of the fundamental physics of electron transport, while laying the groundwork for technological advances at the nanometer scale.