Composting organic waste can reduce greenhouse gas (GHG) emissions by diverting materials from landfills and anaerobic storage, potentially conserving up to 3.1 Mg CO2 equivalent per dry Mg of feedstock. However, the composting process itself emits GHGs, primarily methane (CH4) and nitrous oxide (N2O), as well as air pollutants like ammonia (NH3) and volatile organic compounds (VOCs). Emissions vary based on feedstock composition, moisture content, and environmental conditions. CH4 is often the largest contributor to global warming potential for yard waste composting, while N2O dominates for nitrogen-rich wastes. Mitigation strategies include optimizing composting conditions using additives and improving aeration. Effective pile management and oxygen concentration control are crucial for minimizing CH4 emissions, although forced aeration may increase NH3 emissions in some cases. Additionally, various technologies such as biofiltration can help abate GHG emissions from composting processes. Researchers are exploring innovative approaches to reduce and utilize GHGs in composting, including CO2 adsorption and transformation methods. This chapter highlights the dual role of composting as both a contributor to and a mitigator of GHG emissions, emphasizing the importance of best management practices to minimize environmental impacts while promoting sustainable agricultural practices.