Bioelectrochemical systems (BESs) are considered a new and efficient technology for waste management and bioenergy production. BESs have dual actions to reduce environmental pollution and provide electricity from readily available, sustainable, and cost-effective sources. Microbial fuel cells (MFCs) can efficiently convert chemical energy obtained from organic waste into electric energy. Microbial electrolysis cells (MECs) convert energy into biofuels. Moreover, BESs contribute to the recovery of metals, water, and nutrients. The organic waste that serves as a substrate in fuel cells can be in the form of solid masses or wastewater. The decomposition of solid organic wastes is more difficult than that of organic wastewater. This chapter provides a brief overview of the various types of organic waste used in BESs.