This paper presents comparative technoeconomic and environmental analyses of three ethylene manufacturing pathways based on ethane-rich shale gas, corn stover, and corn grain. The shale-gas-based pathway includes two processing steps, namely, shale gas processing to produce ethane and ethane steam cracking to manufacture ethylene. The two biomass-based pathways also contain two processing steps each, namely, bioethanol production via fermentation and ethylene manufacturing via bioethanol dehydration. A distributedYcentralized processing network that consists of distributed ethane/bioethanol production and centralized ethylene manufacturing is employed for each of the three pathways. Detailed process simulation models are developed for major processing steps, and the three pathways are then modeled on five different ethylene production scales. On the basis of the detailed mass and energy balances and life cycle inventory results, we conduct technoeconomic and life cycle analyses to systematically compare the economic and environmental performances of the three ethylene manufacturing pathways. The results indicate that the shale-gas-based pathway is the most attractive due to the lowest break even ethylene prices ($0.32/kg to $1.67/kg); however, it leads to the highest greenhouse gas emissions of about 1.4 kg CO2-equiv/kg ethylene. On the contrary, the corn-stover-based pathway results in the lowest greenhouse gas emissions of around 1.0 kg CO2-equiv/kg ethylene but the highest break even ethylene prices ($2.0/kg to $4.1/kg). Sensitivity analyses are performed to systematically investigate the influences of parameter deviations on the economic and environmental performances of the three ethylene manufacturing pathways.