Microalgae and cyanobacteria represent a potential source of bioactive compounds, including anticancer compounds, that has yet to be fully explored. This chapter provides a comprehensive review of potential anticancer compounds from microalgae and cyanobacteria of both freshwater and marine origins. Manipulating the growth conditions of microalgae or cyanobacteria, for instance, by imposing different stresses on the cells, could enhance production of biomass with valuable secondary metabolites, including those of pharmaceutical and/or industrial values. Microalgae such as Haematococcus are a potential source of functional ingredients, particularly astaxanthin, which is a potent antioxidant that has been shown to have anticancer activity. There have been two reviews on the anticancer potential of microalgae and cyanobacteria, but the focus was mainly on marine species. A diverse range of bioactive compounds with anticancer effects have been discovered from microalgae and cyanobacteria.