Special Interest Catogories: biotechnology; materials science; medicine; ecology and chemistry. The book summarizes the literature data and research results on biodegradable polyesters of microbiological origin -- polymers of hydroxy alkanoic acids (polyhydroxyalkanoates, PHAs). These polymers are thermoplastic, biodegradable, and biocompatible. They are promising candidates for applications in agriculture, communal services, pharmacology, medicine, and other spheres. The book sums up the most recent data on the known types of polyhydroxyalkanoates, their producers, substrates, and methods of biosynthesis. The structure and physicochemical properties of these polymers, the methods used to process them to make specialised products and spheres of their application are described in the book.