Technical Abstract: Numerous reports exist concerning the production of antifungal compounds by cyanobacteria and algae. However, most reports of antifungal activity by compounds from algae and cyanobacteria concern their evaluation for pharmaceutical activity. There are substantially fewer reports on the evaluation of these organisms for antifungal activity against economically important plant pathogenic fungi. In order to spur new research efforts and suggest possible avenues for future chemical ecology research, we have selected to specifically review the substances produced by cyanobacteria and algae with clearly documented antimicrobial activities against only those species of fungi that are recognized as pathogenic to either plants or algae. This review briefly examines some aspects of algal defense strategies and the pathogenic nature of fungi. In addition we discuss antifungal algae natural products in agricultural pest control and the approaches that we are currently using to discover antifungal compounds from algae and cyanobacteria.