Ongoing interest in exploring alternative options to conventional petroleum based polymers has resulted in significant attention to various biopolyesters, including poly(lactic acid) (PLA) and poly-3-(hydroxy alkanoates) (PHAs), which are bio derived and compostable. However these materials suffer from high production costs, brittle nature, slow crystallization rates and low melt strength, which restrict their processability under common polymer processing operations. Upgrading the properties of these biopolymers is therefore an extremely active area of research in academia and industry, with scientists and technologists striving to match performance of biopolymers with petroleum based polymers to find new applications. The present keynote presentation will discuss our recent efforts to upgrade the properties of biopolyesters through compounding and reactive modification procedures. Specifically we have biologically produced and characterized elastomeric medium-chain-length polyhydroxyalkanoates (MCL PHA), which are then employed as impact modifiers in formulations with PLA and brittle short-chain-length PHAs. Efforts for chain extension/functionalization have included the functionalization of the MCL-PHAs using epoxy functional groups, and mixing with epoxy-based chain extenders. We have found that a simple reactive modification process, involving reaction with a peroxide and coagent improves the crystallization rates and melt strength of PLA and its blends with MCL PHA, as well as improved compatibility between the blend components. This approach has resulted in blends having improved toughness, and processability.