This chapter deals with the production, processing and application of biobased and biodegradable polyhydroxyalkanoates (PHAs), especially poly(3-hydroxybutyrate) (PHB) with a focus on photoautotrophic cultivation of cyanobacteria. PHB is accumulated as a storage compound by a wide variety of taxonomically different bacteria including cyanobacteria, aerobic anoxygenic phototrophic, purple non-sulfur as well as heterotrophic bacteria. Cyanobacteria are photoautotrophic organisms and need to be provided with light, CO2 and mineral nutrients. They can be cultivated in open or closed systems (so-called photobioreactors). After cultivation, biomass is harvested and PHB extracted, where two main methods can be distinguished: polymer solubilization and solubilization of non-PHB biomass. PHB can be processed via extrusion or injection molding and used for various applications, ranging from agriculture/ fishery/gardening and food packaging to applications in medicine or pharmacy. These applications are mainly based on the biodegradability of the polymer. PHB is degraded in soil and liquid environments and even at unfavorable conditions (e.g., low temperature). Some companies produce PHA at a large scale, but quantities are too low to substitute conventional polymers, mainly due to rather high PHAmarket prices. This is, among others, a reason why research focused on the utilization of cheap nutrient sources and thereby on the integration of PHA production into biorefinery.