This chapter discusses the present literature on bacterial polyhydroxyalkanoate (PHA) synthesis, PHA granules, their biogenesis, and structure, and on protein engineering approaches of associated proteins aiming at the design of PHA granules as biobeads for biomedical use. The biologically produced biopolyesters comprise a complex class of polyoxoesters. The nucleotide sequences of 88 PHA synthase genes from at least 68 different bacteria have been attained. Interdisciplinary knowledge is required for further research on the production and application of PHAs. A range of proteins and other molecules have now been successfully immobilized at the surface of PHAs granules; this indicates that these bacterial storage compounds have potential to be developed into powerful tools for diagnostic and therapeutic biomedical applications. One strong advantage of PHA granules as functionalized nano-/micro-beads, apart from simple and cost-effective production, is the oriented immobilization of proteins via the GAP-tag and thus high binding capacity of the resulting beads.