This chapter will review the currently available strategies for interfacing transition metal nanoparticles with enzymes and other more complex biological systems, as well as the applications of such biometal hybrids in the areas of catalysis, energy production, environmental remediation, and medicine. In the first part of this chapter, the focus will be on the many nanometal-enzyme hybrids that have been developed for applications in organic synthesis. Within the field of organic chemistry, nanometal-enzyme hybrids are often used as bifunctional catalysts to mediate different multistep transformations, as for example the dynamic kinetic resolution of alcohols and amines. The second part of this chapter will offer an overview of nanometal-enzyme hybrids that are used as bioelectrodes in biofuel cells. This area of research has grown significantly during the past decades, much because of the many potential future applications of such devices for medical purposes. Here, nanometal-enzyme hybrid based biofuel cells hold particular promise for biosensing applications, as well as for replacing battery-based solutions in actuator devices such as mechanical valves and pacemakers. In the final part of this chapter, the different strategies to use bacteria to synthesize metal nanoparticles will be reviewed. As will be shown by the many examples in this part, biologically synthesized and supported transition metal nanoparticles constitute interesting catalytic systems that could for example be used for energy production, pollutant degradation, and small molecule synthesis.