Microorganisms have always been integral to natural circular processes in the environment. They serve an important role in converting complex biological molecules into central building blocks that can be converted back into complex products. As a society, we now seek similar circularity in the semi-synthetic world that we’ve constructed through over a century of synthetic organic chemistry. Recent advances in genomics and synthetic biology have enabled exploitation of a wide array of microbes engineered to produce value-added products from biomass-derived and synthetically derived substrates. Our group has mainly focused on oleaginous yeast – that use a variety of low-value and waste feedstocks and can naturally accumulate a large amount of lipids. We have engineered multiple genetic tools to rapidly engineer Yarrowia lipolytica, and used these tools to elucidate cryptic metabolic pathways, and to produce oleochemicals and secondary metabolites by taking advantage of naturally high flux pathways. We will also describe emerging oleaginous yeast with more favorable properties for utilizing low-value and waste substrates. Finally, we will describe our recent efforts towards polyolefin and polystyrene degradation and upcycling using microbes from the gut of mealworms.