Technical Abstract: Algae and cyanobacteria (blue-green algae) are prolific producers of secondary metabolites that are a potential source of new pesticides. Previous discoveries of bioactive compounds from algae and cyanobacteria as algicides, herbicides, and fungicides related to agriculture and as pesticides for invertebrate control (insecticides and molluscicides) are discussed. In addition, the approaches that we are using in our laboratories to discover antialgal, antifungal, and herbicidal compounds from algae and cyanobacteria are presented.