Medium-chain-length poly-3-hydroxyalkanoates (mcl-PHAs) were discovered in the 1980s, 60 years after their more famous biopolyester ancestor poly-- -hydroxybutyrate. Accumulated only by a group of related Pseudomonas species, these polyesters are remarkable in their structural diversity and applications. mcl-PHAs are highly water resistant, yet readily susceptible to enzymatic degradation. They can be used in packaging, paints, toners, adhesives and in many biomedical applications but have yet to be produced commercially. mcl-PHAs are most efficiently produced from carboxylic (fatty) acids such as octanoic acid but can also be produced from many nonrelated substrates such as glucose. Recent advances in fermentation and separation processes, as well as strain development are improving polymer quality and reducing production cost, which should soon lead to the adoption of mcl-PHAs by industry.