California’s cap-and-trade program regulating greenhouse gas (GHG) emitters receives revenue from the auction of emissions allowances that, by law, can only be spent on reducing GHG emissions. In order to award these Climate Investments funds to projects that reduce emissions or sequester CO2, state agencies must hae a method for estimating the size of a project’s GHG benefit. This talk describes the development of a quantitative methodology for carbon accounting in riparian forest restoration and conservation to be used by the California Department of Conservation (DOC) . The effort faced a scientific challenge and a policy challenge. On the science side, there were few published data relevant to predicting carbon accumulation in riparian forest stands, and timber models proved inadequate to the task. On the policy side, the challenge was to ensure that funded projects would not maximize carbon sequestration at the expense of other co-benefits (e.g., wildlife corridors, fish passage, erosion control, water quality). We used a mostly unpublished dataset of riparian forest inventory plots of known age to parameterize growth models for live tree biomass over 100 years. We then used these values to estimate accumulation of carbon other ecosystem pools. Results were grouped into look-up tables for carbon sequestration in various riparian forest types and coded into an online estimation tool, CREEC.