Rapid industrialization and urbanization associated with the environment changes calls for reduced pollution and thereby least use of fossil fuels. Biofuel cells are bioenergy resources and biocompatible alternatives to conventional fuel cells. Biofuel cells are one of the new sustainable renewable energy sources that are based on the direct conversion of chemical matters to electricity with the aid of microorganisms or enzymes as biocatalysts. The gradual depletion of fossil fuels, increasing energy needs, and the pressing problem of environmental pollution have stimulated a wide range of research and development efforts for renewable and environmentally friendly energy. Energy generation from biomass resources by employing biofuel cells is crucial for sustainable development. Biofuel cells have attracted considerable attention as micro-  or even nano-power sources for implantable biomedical devices, such as cardiac pacemakers, implantable self-powered sensors, and biosensors for monitoring physiological parameters. This book covers the most recent developments and offers a detailed overview of fundamentals, principles, mechanisms, properties, optimizing parameters, analytical characterization tools, various types of biofuel cells, all-category of materials, catalysts, engineering architectures, implantable biofuel cells, applications and novel innovations and challenges in this sector. This book is a reference guide for anyone working in the areas of energy and the environment.