Electron transfer between proteins in microorganisms and solid materials underpins many aspects of bioelectrochemical energy research. My laboratory seeks to tailor both new microbes and new proteins for specific bioelectrochemical applications. Here I will first describe how we have customized the industrial microbe Escherichia coli for use in biological fuel cells. By transplanting the Mtr pathway of Shewanella oneidensis MR-1 into Escherichia coli, we can confer upon these cells the ability to reduce metal ions, solid metal oxides, and electrodes. These cells couple current production to a metabolic shift towards more oxidized products, demonstrating that we can electronically control the intracellular state of these engineered E. coli. Additionally, we have shown that these engineered E. coli can accept, as well as donate, electrons from an electrode. Thus, this work provides a blueprint to bi-directionally move energy and information between microbial cells and electrodes, and has direct applications in biosynthesis and bioenergy. I will also describe new studies probing the thermodynamic and structural basis by which Mtr proteins reduce solid metal oxides.  We show that MtrF from S. oneidensis MR-1, which can directly reduce iron oxide, binds to iron oxide, but not structurally similar aluminum oxide. Using protein and X-ray footprinting, we also probe which residues of this extracellular electron transfer protein are potentially involved in binding iron oxide. We find that these residues cluster in the tertiary, rather than primary, structure of the protein, suggesting that these regions form a binding site for their solid substrate.  This new understanding will critically inform efforts to rationally design proteins capable of rapid interfacial electron transfer.