Bioelectrochemical systems (BES) represent a novel interface between electrochemical processes and microorganisms, facilitating electron transfer between donors and acceptors. The paper extensively elaborates on the pioneering application of algae in enhancing the performance of BES, particularly in microbial fuel cells (MFCs). Algae serve a vital function through multiple pathways: supplying oxygen via photosynthesis as a final electron acceptor, sequestering carbon dioxide from the atmosphere and anode chambers, cleaning wastewater by removing organic pollutants and nutrients and yielding valuable biomass for biofuel production. This chapter addresses specific BES configurations, including MFCs, Microbial Electrolysis Cells, Microbial Electrosynthesis, and Microbial Desalination Cells, emphasising the extracellular electron transfer pathways and photosynthesis processes that enable these setups. The experimentally observed evidence supports algae-integrated BESs achieving remarkable performance standards, including a maximum power density of 410 mW/m2 and COD removal rates of 74%–86.6%. Moreover, algae-based electrodes are also adaptable as electron donors and acceptors, establishing efficient syntrophic relationships with bacteria that enhance overall system stability and efficiency. Successful utilisation in wastewater treatment, electricity generation, and CO₂ capture, as demonstrated through case studies, establishes algae-based BESs as a promising green bioengineering technology that is both environmentally beneficial and sustainable, generating renewable energy and valuable resources simultaneously.