Genetically-engineered bacteria which produce biodegradable polymers and copolymers with structures which depend oil the culture in which they are kept are receiving increasing attention. Up to 90% of the dry weight of the bacteria can be intracellular granules of the plastic (see Figure), and the properties of the polymers can be controlled by varying the carbon-based nutrition of the bacteria. Recent advances are reviewed, including the use of plants instead of bacteria.