||Enzymatic biofuel cells use enzymes to catalyze electrochemical reactions, directly converting chemical energy to electricity. In this research, three enzymatic biofuel cell devices were created and a focus was placed on their electrode structure in order to improve current density, power density, and/or biocompatibility. The first device, a flow-through glucose biofuel cell, was fabricated from laser-cut poly(methyl methacrylate) and utilized a porous anode to increase current density through improved mass transfer. The maximum current and power density of 705 μA cm-2 and 146 μW cm-2 were among the highest for a flowing biofuel cell in the literature. The second device was a contact lens lactate biofuel cell fabricated in two iterations: one using buckypaper electrodes and the other with carbon paste electrodes, both electrode types being molded into a contact lens. These were the first reported examples of a biofuel cell on a contact lens. The first prototype suffered from poor stability as well as biocompatibility issues, but the second prototype was more stable and amenable to possibly being worn on the eye. The current and power density of the second prototype were, respectively, 22 ± 4 μA cm-2 and 2.4 ± 0.9 μW cm-2 at 0.18 ± 0.06 V. As the device was limited by its cathode, simulations were created to investigate two important factors: carbon nanotube (CNT) connectivity to the electrode and enzyme loading on the CNT surface. It was found that ca. 20% of the CNTs were connected to the electrode; furthermore, only 1-2% of the enzyme was wired to the electrode through the CNT network and roughly 20% of the CNT surfaces were in communication with enzyme. The ferrocene redox polymer/lactate oxidase enzyme-mediator anode system used on the second contact lens biofuel cell prototype performed very well, so it was also used in the third device-a self-powered lactate sensor. Coupled with a bilirubin oxidase cathode, the sensor had a detection range between 0-5 mM lactate, a sensitivity of 45 μA cm-2 mM-1, and a current and power density of 657 ± 17 μA cm-2, 122 ± 5 μW cm-2, respectively.