This review discusses the development and performance of microbial and enzymatic biofuel cells since 1994. Biofuel cells are classified based on electrode reaction types and biochemical processes. The review critically evaluates their performance and explores various applications. While significant progress has been made in enzyme electrode development, biofuel cell engineering has lagged. The paper highlights performance limits and suggests future research directions. Biofuel cells use enzymes or whole organisms as catalysts, operating under mild conditions (20-40°C, near-neutral pH). They are attractive for applications where high temperatures or harsh conditions are undesirable. However, challenges remain in achieving long-term stability and efficiency, particularly with enzymatic systems. Applications include bioremediation, power generation for medical devices, and remote power sources. The review covers both microbial and enzymatic biofuel cells, discussing their mechanisms, performance, and challenges. It also addresses the classification of biofuel cells based on fuel containment, catalysis sources, enzyme origins, and electron transfer methods. The review highlights the importance of mediator molecules in electron transfer and discusses various types of biofuel cells, including those using whole organisms, diffusive or non-diffusive mediators, and enzymatic systems. It also examines the impact of environmental factors on biofuel cell performance and the potential for scaling up biofuel cell systems for practical applications. The review concludes that while biofuel cells show promise, further research is needed to improve their efficiency, stability, and scalability.This review discusses the development and performance of microbial and enzymatic biofuel cells since 1994. Biofuel cells are classified based on electrode reaction types and biochemical processes. The review critically evaluates their performance and explores various applications. While significant progress has been made in enzyme electrode development, biofuel cell engineering has lagged. The paper highlights performance limits and suggests future research directions. Biofuel cells use enzymes or whole organisms as catalysts, operating under mild conditions (20-40°C, near-neutral pH). They are attractive for applications where high temperatures or harsh conditions are undesirable. However, challenges remain in achieving long-term stability and efficiency, particularly with enzymatic systems. Applications include bioremediation, power generation for medical devices, and remote power sources. The review covers both microbial and enzymatic biofuel cells, discussing their mechanisms, performance, and challenges. It also addresses the classification of biofuel cells based on fuel containment, catalysis sources, enzyme origins, and electron transfer methods. The review highlights the importance of mediator molecules in electron transfer and discusses various types of biofuel cells, including those using whole organisms, diffusive or non-diffusive mediators, and enzymatic systems. It also examines the impact of environmental factors on biofuel cell performance and the potential for scaling up biofuel cell systems for practical applications. The review concludes that while biofuel cells show promise, further research is needed to improve their efficiency, stability, and scalability.