The California Climate Action Registry (Registry) is developing a protocol for quantifying greenhouse gas (GHG) emission reductions from projects that target changes in manure management on livestock operations. The project protocol provides essential steps for demonstrating credible emissions reductions using transparent and practical approaches. There are a number of key decision points in developing a project protocol such as how to define the project and its boundaries, determining eligibility and additionality, characterizing baselines, quantifying baseline and project emissions, estimating reductions, and verifying project performance. Research on GHG emissions in agriculture, data on manure management practices in California, and review of existing project protocols are foundational to the Registry’s protocol. This presentation will give a preview of key features in the protocol, focusing on the data-driven process of developing a performance standard to assess project additionality.