Biopolymers are gaining attractivity for the production of both commodity and speciality chemicals. Microorganisms are able to produce a large variety of biopolymers, of which some are already produced and others need to be further characterized, and even to be discovered. This review article focuses on biopolymers such as polyesters (polyhydroxyalkanoates (PHAs), polysaccharides and proteins due to their ability to provide appealing alternatives to the already established variety of fossil-based polymers. Furthermore, these bio-proteins can also stand as alternatives to proteins from agriculture. Producing microbial biopolymers from organic wastes, and by-products, by using open mixed microbial cultures (MMC) has been suggested in order to reduce production costs as well as give the waste a new resource status. MMC strengths and weaknesses analysis has shown that this system might be relevant for producing a variety of microbial polymers in the view of complex feedstock applications. Original principles have already been developed for orientating the microbial community towards certain functionalities and the research undertaken on this topic is still very active. In this present review article, we critically examine microbial enrichment strategies, discovered these last decades, to make the biopolymer production by open MMC an industrial reality.