Over the last 40 years, researchers have been studying and improving enzymatic biofuel cells, but until the last five years, the technology was plagued by short active lifetimes (typically 8 hours to 7 days) that prohibited the commercial use of this technology. This tutorial review introduces the topic of enzymatic biofuel cells and discusses the recent work done to stabilize and immobilize enzymes at bioanodes and biocathodes of biofuel cells. This review covers a wide variety of fuel systems from sugar to alcohols and covers both direct electron transfer (DET) systems and mediated electron transfer (MET) systems.