Polyhydroxyalkanoates (PHAs) are biopolymeric intracellular inclusions that serve as carbon and energy storage compounds for diversified microorganisms. PHAs are synthesized by a variety of bacterial strains such as Alcaligenes latus, Azotobacter vinelandii, Pseudomonas sp., and Escherichia coli under limited oxygen but sufficient availability of carbon source. Rubber-like nature along with biocompatibility, biodegradability, eco-friendly, renewable, and biological production features make the PHAs as promising alternatives to synthetic plastics which can mitigate plastic-waste disposal mediated environmental pollutions. However, carbon source requirement driven high production cost and low yield limit the large-scale production of bioplastics and so as to its wider applications. For minimization of production cost, many researchers focused on utilization of waste/by-product based carbon sources for PHA biosynthesis. On the other hand, several other researchers emphasized on the exploitation of genetically engineered microbes and plants to address the low yield issues. Consequently, these attempts of improvements will be helpful in making the bioplastics more competitive than the conventional ones in long run. In addition to their common use as bioplastic, PHAs are widely used in various fields, including medical, pharmaceutical, agro-industries, textiles, households, etc. This chapter provides an overview of classification, structural components and properties of microbial PHAs, progresses in PHA biosynthesis, highlighting different biosynthetic pathways, role of various substrates, microorganisms, and experimental parameters on PHA biosynthesis. Recent advancements in enhancing the physico-chemical properties of PHAs and trends in agro-industrial applications of PHAs have also been discussed. Futuristic approaches to overcome the challenges associated with the yield and improved mechanical properties of PHA are also recommended in this chapter.