Since the initial discovery of marine phyco-derived secondary metabolites in the 1950s there has been a rapid increase in the description of new algal natural products. These metabolites have multiple ecological roles as well as commercial value as potential drugs or lead compounds. With the emergence of resistance to our current arsenal of drugs as well as the development of new chemotherapies for currently untreatable diseases, new compounds must be sourced. As outlined in this chapter algae produce a diverse range of chemicals many of which have potential for the treatment of human afflictions.In this chapter we outline the classes of metabolites produced by this chemically rich group of organisms as well as their respective ecological roles in the environment. Algae are found in nearly every environment on earth, with many of these organisms possessing the ability to shape the ecosystem they inhabit. With current challenges to climate stability, understanding how these important organisms interact with their environment as well as one another might afford better insight into how they respond to a changing climate.