As for any other biotechnological process, PHA production with photo-autotrophic microorganisms demands short fermentation times, high volumetric productivity, simple handling, low risk of contaminations and low operating cost Cyanobacteria cope with most of these criteria. They became, especially in the period 1980 – 2001, the central research topic of many working groups worldwide (see Table 1). Strains and cultivation conditions were improved for significantly shorter fermentation times and impressive high PHA contents. More specifically, all authors report PHB to be the dominant, if not the only poly(hydroxyalkanoate) in cyanobacteria. Another storage product is the carbohydrate glycogen which is produced growth associated and in competition for the acetate pool with PHB synthesis.8